The hosts are now one point from overtaking Liverpool's league tally after a commanding performance which leaves their opponents trophy-less and boss Ancelotti under pressure
Manchester United moved within one point of a record 19th league title as they saw off the challenge of champions Chelsea with a 2-1 win at Old Trafford.
A goal after 36 seconds from Javier Hernandez and a header from Nemanja Vidic were enough for the hosts, who were dominant throughout, although Frank Lampard made it a nervous ending with a goal 20 minutes from time.
For Chelsea, it was a disappointing display after battling their way back into the title race and they will have to hope that both Blackburn Rovers and Blackpool can somehow beat United to prevent them from taking the Premier League crown away from Stamford Bridge.
It was another commanding display by United, with superb performances coming from all over the pitch, in contrast to the opposition who could not match their energy despite having an extra man in midfield.
Sir Alex Ferguson wrote in his programme notes beforehand that Carlo Ancelotti should be kept on as Chelsea boss next season, but after this performance club owner Roman Abramovich might take a different view.
As expected, Didier Drogba was preferred to Fernando Torres at head of the Chelsea attack, with Saloman Kalou given a start on the wing as a reward for his winner against Tottenham.
United were forced to bring in John O’Shea at left-back as Patrice Evra was forced to miss out with a thigh injury and Hernandez, who scored the last time the teams met in the Champions League, was once again chosen to partner Wayne Rooney up-front.
Not long ago, the visitors were 15 points behind and looking like it was going to be a trophyless season, but they came into the match with the chance to move back into first place.
Remarkably, though, the league leaders were 1-0 up after 36 seconds and it was the two players who had scored in their recent Champions League meeting who combined to give United the lead.
Park-Ji Sung moved into the Chelsea half before slipping a through-ball past the outstretched foot of David Luiz into the path of Hernandez, who confidently slotted past Petr Cech to send the home fans into raptures.
Ancelotti remonstrated with Luiz straight after, but things didn’t get any better for the Brazilian defender who endured a torrid afternoon, in marked contrast to his goal in the reverse fixture.
The visitors were stunned and they had to be grateful for a flying save by Cech to his right to keep out a Rooney shot from around 30 yards which was heading straight into the corner.
It was one-way traffic and Hernandez came close to scoring again. Ryan Giggs dribbled his way to the edge of the Chelsea box, before laying it off to Park who curled in a lovely cross first-time which landed over Luiz and just evaded the Mexican striker who arguably should have got something on it.
The away side’s frustrations were encapsulated by a nasty lunge from Branislav Ivanovic which upended Rooney and earned him a yellow card that was not argued against.
The energy of players such as Park and Rooney were giving the Chelsea players no time on the ball and the England striker came close to scoring again when he dragged his shot form the edge of the area just wide of the right-hand post.
The impressive Park was more than justifying his selection ahead of Nani on the wing and he won a corner after his swerving shot from the left was parried by Cech at his near-post.
And from the corner, the home side scored the second goal their opening quarter of the match deserved. Giggs took it short and after stepping past Kalou he whipped in a brilliant cross which went over the head of Luiz and was headed home by Vidic.
However, the lead was nearly halved immediately, Chelsea winning their own corner which was flicked on by John Terry for Kalou to head straight at Van der Sar from a few yards out, before Ivanovic flicked the rebound into the side netting from a tight angle.
On the half-hour mark, Kalou was tripped around 30 yards from goal and Drogba stepped up to hit the free-kick over the wall and towards the bottom corner, but Van der Sar got down low his left to parry it away.
Moments later, he had another free-kick from a few yards further in on the other side, but this one fell comfortably wide of the goalkeeper’s right-hand post.
With five minutes left of the first half, Ivanovic once again tripped Rooney who spent a long time on the ground, but referee Howard Webb ignored the chants of the crowd and decided to keep the Serbian on the pitch rather than brandish a second yellow.
Antonio Valencia and Rooney played a one-two which set the winger free down the right-hand side and only a last-ditch sliding tackle from John-Obi Mikel prevented Hernandez from reaching his cross in front of goal and putting the game to bed before the break.
The visitors' half was summed up when a clearance by Giggs was dribbled out for a United corner by Essien under pressure from the indefatigable Park.
The half-time whistle was blown soon after to loud cheers from the Old Trafford crowd, who knew they already had one-hand on the Premier League trophy.
With goals needed in the second half, Ancelotti resisted the temptation to bring on Torres or Nicolas Anelka, instead bringing on Ramires and Alex for Mikel and Luiz, whilst the hosts replaced the injured O’Shea with Jonny Evans.
Chelsea started the second period in much brighter fashion, but they were extremely fortunate not to give away a penalty, as Valencia’s cross hit the outstretched hand of Lampard who was diving in to block it.
Moments later, Kalou went over in the United penalty area after contact by Vidic, but again nothing was given by the officials.
On the hour mark, Ancelotti threw on Torres as his last throw of the dice, replacing Kalou, but the away side’s only threat was coming from Drogba, who hit a shot narrowly wide although only after using his arm to control the ball.
But from nowhere the champions grabbed a goal back, as Ramires’ cross deflected off Evans before being flicked on by Ivanovic to Lampard, who poked in from a few yards out.
The two-goal lead was almost immediately restored, though, as Ashley Cole was robbed by Valencia. The ball fell to Hernandez who squared it to Rooney, but his tap-in was impressively blocked by a diving Alex when it looked like the ball was going into the net.
Lampard’s goal left the visitors 20 minutes to try and salvage their season and although they started to improve, they were thwarted by a well-drilled United defence.
In a frantic last 10 minutes, both teams had chances to score, with Rooney having three in the quick succession.
His first effort from the edge of the box was dragged wide, then he was through on goal but after rounding Cech his shot was saved before moments later having a shot deflected over by Alex.
Hernandez had an even better chance a few minutes later, but he headed Valencia’s drilled cross over the bar from six yards out.
Torres had been largely anonymous since coming on, but he had a chance to salvage a point for Chelsea, but his shot from just inside the box was dragged wide, before Hernandez reciprocated at the other end.
The home side were eventually able to close the game out relatively comfortably and effectively seal a record-breaking 19th English title.
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