The Barça hymn booms out immediately after teh referee's whistle to mark an emphatic win for Barcelona and it is hugs all round between the players. They will meet again next week, but the Blaugrana now head to Germany knowing that a semi final place is theirs to lose.
Huuuyyy!!! - Iniesta clipped the ball over to the far post where Messi controlled and took aim, but his shot was blocked en route to the net by the head of Keita who looked stunned to have been the one to block a fifth goal.
Marquez is booked for time wasting and it was certainly deliberately as he will now miss the second leg next week and not the semi final.
Yellow Card Rafa Márquez
Substitution Eto'o Bojan Krkic
Huuuyyy!!! - Marquez looks to add his name to the scoresheet after moving forward, but his drive flew just wide of the far post.
Oddo is very lucky not to concede a penalty as Iniesta eased past him before being shoved by the Bayern defender as he looked to cross the ball.
Ribery embarked on his best run of the game and sent over a low crosss that was cleared back to him. The Frenchman looked for a short pass to a team-mate, but incredibly Eto'o was back defending and cleared.
Oddo needs some treatment and then limps to the sidelines before Barcelona take the throw-in and begin to build once more through the midfield.
Barcelona may not have been able to maintain the intensity of their first half play, but with the game, if not the, tie alrady won there wil be few critics of this second half display.
Sergi Busquets receives his instructions from Guardiola, who is leaning over from the seats behind the bench, and the nidfield then goes on to replace Toure Yaya. Bojan is still warming up.
Substitution Yaya Touré Busquets
Huuuyyy!!! - Iniesta takes down the ball with one touch and then slaloms into teh area before lifting the ball just over Butt's bar.
Puyol must wonder what Iniesta thought of him as he played a ball far too hard down the flank moments before Bayern made their second change with Jose Sosa coming on for Ze Roberto.
Substitution Zé Roberto José Sosa
Henry is the first player to make way for Barcelona as he receives a standing ovation as he heads, somewhat begrudgingly, towards the bench to be replaced by Seydou Keita.
Cheers greet every touch by a Barcelona player as they roll the ball around the pitch, but they can still not find a way to a fifth goal.
Substitution Thierry Henry Seydou Keita
Ze Roberto looked set to make up for his earlier lack of control after receving the ball in front of goal, but an incredible tackle from Puyol saw his effort ricochet wide of the target. A superb block.
Ze Roberto was picked out by Ottl, but he could not control the ball when on th edge of the area with only Puyol between him and the goal.
Barcelona lok set to make a change as Valdes is called up on to come off his line to meet a cross, but he was unchallenged and his long punt down field immediately puts the pressure back on Bayern.
Even one away goal would give Bayern something to work with in the second leg next week, but they cannot even find a way to test Valdes in the Barça goal, let alone score past him,
Barça see a corner cleared moments after they had mounted another attack following Eto'o's drive from distance that flew well over the bar.
Toni is not having much luck as he is stopped in his tracks for committing two fouls and he is beginning to look more and more frustrated trying to find a way through Marquez and Pique.
Huuuyyy!!! - The save of the game without a doubt as Messi edged along the area before releasing a drive that Butt met with a hand and diveted the ball up and on to the crossbar. A great shot and an incredible stop.
Yellow Card Martín Demichelis
Toni just attempted a shot from 20 yards, but it travelled just two yards before hitting Marquez as even Bayern's forward appear to be short of ideas as they try to work out how to cope with the Blaugrana.
Barcelona have settled intp passing the ball just in front of the Bayern area while they probe for yet anorher opening. The Germans are happy to just sit back and hope to soak up the pressure.
The game is being played at a slightly slower pace, but that is no surprise given the lead that the hosts have and the effort they put in during the first 45 minutes to chalk up four goals.
Henry does not have many chances to pass players in la Primera and he is enjoying himself against the cumbersome Oddo. After passing him this time, the French forward is shoved over and wins Barça a free-kick on the left flank.
Toni feels that he should have had a penalty as he moved forward meet Oddo's cross only to go down under a challenge from Marquez, but the linesman had already flagged for offside.
Messi took on Van Bommel and after passing him looked to go past Lell, but the Argentinian was clipped down and the German defender was booked for his troubles.
Yellow Card Christian Lell
Ribery looked to adance down the left flank, but was comfortably stopped by Alves and teh Frenchman has been unabel to show what is capable of this evening.
Barcelona kick off and expectations are high, but surely things cannot be any better than whayt the first half saw. Bayern have brought on Andreas Ottl.
Eto'o maeks way for Bojan Krkic and the Caleroonian striker receives a standing ovation after an outstanding performance.
Substitution Hamit Altıntop Andreas Ottl
The referee blows the wihstle for half-time and Barcelona have been incredible against a Bayern side that came to defend, but have been out maneouvred at every turn. What the Germans can do now is anyone's guess, while the Blaugrana will not want to take their foot off the pedal.
Barcelona continue to press, but with half-time approaching they know that they know that they have done their jobs and proven why they are being billed as the best team in the world at the moment.
Huuuyyy!!! - It was almost five before the break as Iniesta was picked out on the right and he found Messi who in turn pciked out Alves. The Brazilian pushed down the line and his low cross hit Bayern legs before Iniesta shot wide.
Huuuyyy!!! - Toni and Robery play a neat exchange to see the Frenehcman released in the area, but from an angle he slides a shot wide and the Barcelona fans have to stop themselves from whistling.
Messi required treatment after the move as television shows that he was clearly caught by Van Bommel's elbow as the referee allowed play to flow. A good decision by the matchday official, but questions over whether the blow was deliberate.
GOOOAAALLL!!! - Barcelona are running away with this as a flowing move involving Messi, Iniesta and Eto'o finally sees the ball roll out to Henry on the left and the Frenchman slotted it past the stationary Butt.
Goal Thierry Henry
The incredible movement of the ball between the Barcelona team has Bayern chasing them all over the pitch as the fans chant in the stands as they appreciate the dominance of their team.
Huuuyyy!!! - Well, it could have been a huy! as Henry took aim from 25 yards, but blazed his shot over before apologising to those around him. But it was worth a try.
Klinsmann came off his bench with a look of astonishment mixed with annoyance and any ideas he may have had to change his tactics, may have to be rethought after that goal.
GOOOAAALLL!!! - Henry edged down the left of the area and after moving past Oddo his low centre was met in the middle by Messi, who himself beat Lell to the ball. Barcelona are now in complete control on the pitch and on the scoreboard.
Klinsmann will have to decide at the break whether to maintain this system after the break or whether to try and take the game to Barça slightly more to try and net the valuable away goal.
This time Alves looks to be the provider as he lifts a swirling cross into the far post and even though it was too high for Eto'o', Oddo nodded it out for a corner.
Barcelona have taken their foot off the pedal just slightly and Bayern are able to sit off as Alves takes aim from 25 yards and sees his drive fly high and wide of the far post.
Bayern put together their first string of passes that saw them advance in numbers, but the move ended with Barcelona able to step up and catch them offside. but one goal for the visitors would open this tie up again.
The game has quickly regained its rhythm after the stoppage and Barcelona are pressing again down the left as Henry sends in a low cross that Butt meets before Eto'o can.
Ribery has seen his chancs to shine somewhat restricted so far as the predicted duel between him and Messi for the starring role has only seen the Frenchman able to push up after carrying out his defensive duties tracking back.
The fact that there is blood coming around Hans-Jorg Butt's head proves that the facial injury is bad, but he is up and ready to continue with onle slightly puffy, red cheek.
Henry and the keeper collided in the incident and while the Frenchman has injured his ribs, the German custodian received athe sole of a boot in the face and needs treatment too.
Huuuyyy!!! - Iniesta slotted the ball inside the Bayern defence yet again, this time on the left and Henry raced forward before clipping the ball just past the far post.
Eto'o was fouled as he ran forward, but the referee played the advantage before Messi lost possession, while television images show that Guardiola has in fact sat just behind the dug out. Surprisingly there were spare seats.
Guardiola has gone down the tunnel after being sent to the stands for his outburst to both the fourth official and the linesman and he will have to contain his anger from the upper echelons of the Camp Nou.
The Catalans are indignant about the decision by Howard Webb, but Barcelona's continuing forward movement has made them quickly forget about that.
Messi goes down after colliding with Christian Lell in the area, but instead of awarding a penalty, the Argentinian is rightly shown a yellow card for diving. There was contact, but he was looking for it and made the first touch. Guardiola is not happy.
Yellow Card Messi
Huuuyyy!!! - Altintop was unaware that Xavi was lurking behind him as he tried to clear his lines and passed the ball straight to the Barça star, who looked up but could only drive it well over the bar from an angle.
Bayern look rightly stunned by the start that they have endured as they clearly came into the game looking to contain Barcelona early on while trying to nick a goal. Instead, they have been unable to hold out and are already facing a struggle.
Few Bayern defenders claimed for offside, but there were question marks which the televisions around the press area have shown were right to be asked, but Eto'o was level when the ball was played.
GOOOAAALLL!!! - Barcelona are already proving why they are one of the favourites to win the trophy as they take a two-goal lead. A break at speed saw Messi slip the ball behind the defence and Eto'o was able to put the ball through the legs of the approaching keeper.
Van Bommel sees a drive go well wide, before Ribery does little to endear hiself to the fans that he may soon call his own as he launches himself into a challenge with his foot up on Rafa Marquez.
GOOOAAALLL!!! - Iniesta found Eto'o on the edge of the area and the Cameroonian international slipped a pass to Messi who clamly took one touch and rolled the ball beyond the keeper and inside the far post to put Barcelona ahead.
Bayern show that they could pose Barça problems at the end as Ribery and Ze Roberto combine with the latter, ignoring jeers because of his Real Madrid background, to place a cross into the area that Schweinsteiger just failed to connect with.
A sudden spell of Barcelona pressure has Bayern struggling to kick the ball clear, while the home fans are unhappy that the English referee employed Premier League thinking to ignore a strong challenge on Messi.
Huuuyyy!!! - Xavi produced a stunning pass in behind the Bayern defence and Henry raced into the area before rounding the keeper, but he had pushed the ball too far wide and his shot was cleared off the line for a corner.
Barcelona are probing down both flanks and when Alves pushes forward, Franck Ribery drops back to show that he prepared to play for the team.
The rain continues to come down in Camp Nou and it is a bit chilly too, but that will only bother those that have seats without a cover.
The four midfielders of Bayern are already showing that they are all going to work together to squeeze the space in which the Barça midfielders normally do their best work.
Bayern Munich kick off wearing their all white away kit, while Barcelona quickly close them down wearing their traditional home colours of blau and grana.
The two teams have scored 48 goals in 16 matches in the Champions League between them this season, so this should be entertaining to say the least. Follow the action on Goal.com...
The Camp Nou is a full house for this encounter and the Barça hymn booms out before the Champions League quickly follows it while the players line-up before the tradtional handshake.
Jurgen Klinsmann has had to shuffle his team around and looks set to play a slightly reserved line-up with a 4-1-4-1 line-up that sees Luca Toni ploughing a lone furrow up front, while Mark Van Bommel plays in between the defensive and midfield lines.
Pep Guardiola has named what many would consider to be his strongest team for the game with Dani Alves back in the defence, Toure Yaya back in the midfield and Thierry Henry and Lionel Messi back up front after they all mised out at the weekend.
Thousands of Catalans that were due to go away for Setmana Santa have cut their holidays in two in order to be back in the city for this match, rather than giving up their tickets to friends.
The visiting Bayern fans have seen little typical Mediterranean weather sa they have been at teh Fans' Zone in the Port Olimpic area of the city eating German food and drinking beer.
It has been raining in the Catalan capital again today after a torrential day on Tuesday saw the pitch in Camp Nou soaked ahead of the game.
Times In BST
Live Final scheduled Suspended Cancelled Postponed