Alexandre Pato double defeats Inter in what could potentially be a title-deciding result.
Pato opened the scoring in the first minute with a tap-in before Cristian Chivu dealt his sides' chances of a comeback a huge blow on 53 minutes when he was sent off for tripping Milan's goalscorer. The result was put to bed on 62 minutes when Pato doubled his and Milan's tally.
Substitute Antonio Cassano completed the rout on 89 minutes, coverting a penalty he won himself before the former Sampdora man received his marching orders in the 92 minute for a second-yellow card.
The result sees Milan increase their lead over Inter at the summit of Serie A to five points with only seven games to go.
Milan made a dream start to the 154th Serie A Milan derby when they opened the scoring after only 42 seconds. Gattuso slid a defence-splitting pass through to Robinho who failed to round Julio Cesar who could only knock the ball into the path of Pato who slammed home from six yards out.
The game continued to fly by at a frenetic pace and Milan in particular were impressing. A strong claim for a penalty was turned down by the referee, Nicola Rizzoli on nine minutes when Robinho met Ignazio Abate's deep cross with a ferocious volley from 15 yards which was blocked by the arm of Maicon, which was adjudged to be accidental.
Inter got their first real sight of goal on 19 minutes when Thiago Motta won the ball cleanly off Mark van Bommel before steaming forward and laying it off to Giampaolo Pazzini. The former Sampdoria man then powered past Gianluca Zambrotta before poking a low shot from 12 yards that was smartly blocked by Christian Abbiati.
The Rossoneri nearly doubled their lead on 37 minutes although would have done so with a slice of luck. Van Bommel struck a thunderbolt from 30 yards out which took a hefty deflection off Andrea Ranocchia, in the process wrong footing Julio Cesar before smashing the top of the crossbar.
A minute later, their bitter rivals believed they had levelled the scoring when Wesley Sneijder delivered an inviting corner which was met by the head of Motta on the six-yard line. 80,000 people in the San Siro believed an equaliser was inevitable only for Abbiati to somehow claw the ball to safety off the line, a wonderful save celebrated by the 'keeper as if he had just scored the winning goal.
The second-half resumed at an exciting pace although in the 53rd minute, Leonardo's men were dealt a huge blow with the sending-off of Cristian Chivu. Pato was sent through clear on goal and with the Brazilian looking to lift the trigger on the edge of the box, the Romanian defender clipped his heels to send Pato sprawling on the edge of the box with Rizzoli having no alternative than to show the former Roma man the red card in his top pocket.
Thiago Silva blasted the resulting free-kick at goal but Julio Cesar parried the ball into the path of Kevin-Prince Boateng who could only fire the ball high and wide of the goal.
The Nerazzurri's hopes of a comeback were all but extinguished on 62 minutes when Milan doubled their lead. Clarence Seedorf found Abate in plenty of space of the right-side of the Inter box who saw his shot-come-cross headed into the empty net by Pato from six-yards out for his 11th Serie A goal of the season.
It was nearly three on 66 minutes when substitute Mathieu Flamini found Robinho who turned Ivan Cordoba before hitting a powerful effort towards goal that was expertly blocked by Julio Cesar.
Milan continued to lay siege to the Inter goal and should have put the result beyond doubt on 72 minutes when the terrific Seedorf did well to dispossess Ranocchia before sliding the ball to Robinho who despite his quick feet, could not beat Julio Cesar who turned the ball around his post.
Inter's night went from bad to worse when Javier Zanetti blocked off Antonio Cassano in the box on 89 minutes with a penalty being awarded. The substitute stepped up to take the penalty himself, calmly sending Julio Cesar the wrong way to give Milan a 3-0 lead.
Cassano was sent-off in the 92nd minute for a second yellow card for needlessly bringing down Cordoba in the final stages of the game.
Massimiliano Allegri's men travel to Florence next weekend to play Fiorentina while Inter are back at the San Siro midweek for their Champions League quarter-final versus Schalke.
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