Surprise return for Paul Scholes in a Manchester United shirt and Sir Alex Ferguson waves off Wayne Rooney rumours.
Vincent Kompany red card to be challenged by Manchester City
And manager Roberto Mancini accused the United goalscorers, Wayne Rooney and Danny Welbeck, of getting the Belgian red-carded for his 12th-minute challenge on Nani.
Unless an appeal succeeds, Kompany, who was also dismissed against Wolves in October, will serve a four-match ban, and miss both legs of the Carling Cup semi-final against Liverpool and the Premier League meetings with Wigan and Tottenham.
But Mancini said: "We will appeal. I'm sure that we will win an appeal. Can you can explain to me for which reason this was a red card?"
The Italian, who also believed his side should have had a penalty when Aleksandar Kolarov's cross hit Phil Jones on the arm, limited his comments about referee Chris Foy for fear the FA would take disciplinary action against him.
He added: "I don't want to talk to the referee because I want to stay on the bench for the next month."
Mancini courted controversy by brandishing an imaginary card when Liverpool's Martin Skrtel fouled Yaya Toure on Wednesday before he subsequently apologised for his actions and he believed that Rooney and Welbeck were guilty of the same offence. "Probably if you watch the situation again [you will see it]," he added.
But Manchester United manager Sir Alex Ferguson supported Foy's decision to dismiss Kompany. "I think the referee was right," he said. "It was a two-footed tackle. It was a red card, absolutely - I've seen him do it before. Maybe he's got off with it in the past, but the intent was there. Nani is very lucky. It could have been a bad one."
Rooney scored twice before both he and Ferguson angrily denied reports that the striker will leave United.
"Everything that has been in the press of late has been a load of nonsense," said the 26-year-old Rooney "Because it's me, because it's Man United, it has been [taken] out of context, but there is no problem for me. I want to be at this club for a long time."
The manager added: "Today was a magnificent performance. Wayne Rooney is a headline maker. Good or bad, the press don't mind. It is the situation that existed many years ago with Paul Gascoigne. We have seen the good stuff today. Any flaws will be absolutely annihilated by the press. That is what they are like. That is what we are dealing with."
The game was notable for the reappearance of Paul Scholes, who retired at the end of last season but returned for the last half-hour as a substitute.
And Rooney admitted it even took the United players by surprise. He said: "It was a bit of a shock. We didn't know until we were in the dressing room. It's great. It gave everyone a lift. He's a fantastic player and showed his quality when he came on."
Ferguson said: "Paul came to see me and said: 'I regret retiring'. There are no negatives for me. The players have been delighted. I am delighted. The fans are delighted. It is a terrific addition to our squad at a very important part of our season. He is the best at slotting straight in. He is the one who didn't make mistakes."
The United manager was critical of his players for conceding twice to 10-man City in the second half, saying: "We were so careless. It was ridiculous."
However, Mancini described his side's comeback, which included goals from Aleksandar Kolarov and Sergio Aguero, as "two steps forward" and believed it will strengthen their title challenge.
"If we play like this and we have the same attitude, the same strength in every game we will win the league," he said.
Elsewhere, Chelsea defeated Portsmouth 4-0, Sunderland emerged 2-0 winners at Peterborough and League One Sheffield Wednesdayshocked Championship side West Ham United 1-0.
The fourth-round draw threw up another Premier League must-see as Manchester United were paired with Liverpool. Arsenal could face Aston Villa if the London club can find a way past Leeds United tonight, Everton will host Fulham and Chelsea could travel to QPR if the London club emerge from their third-round replay against MK Dons.
Swindon Town's reward for beating Wigan is a trip to either Nottingham Forest or Leicester City.