Chelsea blew the title race wide open when they came from behind to beat Premier league leaders Manchester United 2-1 thanks to Frank Lampard's controversial 79th-minute penalty at Stamford Bridge on Tuesday.
United had deservedly led through Wayne Rooney's 29th-minute strike but Chelsea's Brazilian defender David Luiz equalised nine minutes into the second half with his first goal for the club since joining from Benfica in the January window.
The champions, unbeaten at home against United since 2002, surged forward after that and took the points when Chris Smalling tripped substitute Yuri Zhirkov and Lampard fired home a penalty United manager Alex Ferguson described as "soft."
United remain top on 60 points, four clear of Arsenal but with the London side now having a game in hand. Manchester City are third on 50 with champions Chelsea up to fourth on 48.
"It was a great performance by us. We didn't deserve that," Ferguson told Sky Sports. "It's three years in a row the referees' decisions have changed the game.
"I'm proud of my players tonight, they've endured a lot of decisions against them and they've done their best."
MISERABLE NIGHT
Defender Nemanja Vidic's stoppage-time red card for a second booking completed United's miserable night and the Serbian defender will miss Sunday's trip to face Liverpool at Anfield.
Ferguson felt Luiz should also been sent off for a robust challenge on Rooney and Chelsea coach Carlo Ancelotti said the defender "could have been lucky."
However, the Italian was pleased with his side's commitment, saying: "The performance was really good. If you do not play well you cannot beat Man Utd."
The fixture that has so often been billed as a virtual title decider in recent seasons initially had something of a low-key feel about it with Chelsea unaccustomedly so far adrift of their rivals and their hopes of retaining the title long gone.
Ancelotti opted to go with Fernando Torres and Nicolas Anelka as his front men, leaving Didier Drogba on the bench.
Alex Ferguson also permed two from three with Rooney and Javier Hernandez starting together, with Dimitar Berbatov among the substitutes. It was the same strike force from Saturday's 4-0 win over Wigan Athletic.
The manager said before the game that Rooney was fortunate to be playing having escaped a ban for his off-the-ball elbowing of Wigan's James McCarthy but he was not the only pantomime villain on show as United gave a special welcome to Ashley Cole.
The England defender had been fined and investigated by the police for shooting a member of the Chelsea staff with an air gun at their training ground. One United fan held up a sign saying: "Don't shoot Ashley" while all of them roared "shoot" every time he touched the ball.
In an open, attacking game, United gradually took control and Rooney should have put them ahead when he mistimed a header after 21 minutes.
MORE ENERGY
He made amends eight minutes later when he collected the ball 25 metres out, turned in acres of space and drove a fierce low shot beyond Petr Cech into the bottom corner.
Chelsea showed more energy after the break and levelled after 54 minutes when Ivanovic headed a deep cross into the path of Luiz and the Brazilian defender waited for it to drop before expertly slamming a shot past Edwin van der Sar.
Drogba replaced Anelka after an hour while Berbatov went on for Hernandez 10 minutes later. Ryan Giggs also joined the fray for his 606th league game, equalling Bobby Charlton's United record set on the same ground in 1973.
Chelsea begun to control more of the ball, forcing United to defend deep and it was another substitute, Zhirkov, on in the 71st minute for Florent Malouda, who turned the game when he went down under the challenge of Smalling.
Lampard dispatched a powerful penalty and Chelsea, instead of trailing the leaders by 18 points, are now 12 adrift and back in the Champions League places.
