Javier Hernandez's injury-time goal on Wednesday gave Manchester United a 4-3 win over Newcastle and a seven-point lead in the Premier League following Man City's loss.
United trailed three times at Old Trafford before Hernandez's half-volley completed the comeback and ensured the 19-time champions will enter 2013 with a sizable lead over their Manchester rivals after City's 1-0 defeat at Sunderland.
Jonny Evans, Patrice Evra and Robin van Persie all equalized for United after strikes from James Perch and Papiss Cisse plus an own goal from Evans had put Newcastle in front in a match played in driving rain and featuring several contentious decisions.
"It tells you about the courage of our team ... we had a lot of bad decisions against us in the first half," United manager Alex Ferguson said. "That could have demoralized the team, but they didn't give in. That is the great quality they have.
"We were down three times and came back three times, then we scored the winner. It is a really significant result for us. It puts us in a good position."
Newcastle took a shock lead in the fourth minute when Demba Ba's 25-meter shot was parried by goalkeeper David de Gea into the path of Perch, who slammed the ball into the net.
United struggled to immediately impose itself in the sodden conditions but Evans finally equalized in the 25th, tapping in the loose ball from six meters out after Hernandez's shot had been blocked by goalkeeper Tim Krul.
Three minutes later, Evans turned the ball into his own net to put Newcastle back in front despite the linesman raising his flag with Cisse in an offside position. Referee Mike Dean consulted with linesman Jake Collin and then awarded the goal after a delay of a few minutes, much to the fury of the Old Trafford crowd.
The decision also infuriated Ferguson, who remonstrated with Dean, Collin and the fourth official just before the start of the second half.
"The referee changed the linesman's mind," Ferguson said. "He said it was an own goal. But if you see it again, and the referee can't, the guy is in an offside position, then he pulls Evans' arm. If that is not interfering, what is? I think it was a bad decision."
It could have been worse for United not long after the goal. Newcastle midfielder Sylvain Marveaux struck the crossbar from a free kick just outside the box in the 39th with a fierce left-footed strike.
United equalized in the 58th when Evra sent a low shot beyond Krul after a poor headed clearance from Ba, but Cisse restored Newcastle's lead in the 69th with a powerful first-time shot from inside the box after an error from the hosts' defense.
The lead lasted less than three minutes. The ball fell to Van Persie in Newcastle's box, and Krul was helpless to stop the Netherlands striker from notching his 13th league goal of the season to draw level with Swansea forward Michu as leading scorer.
United and Newcastle had chances to score as the match drew to a close, but it was Hernandez who popped up to provide the dramatic final twist from a through ball by Michael Carrick.