Defending champion Manchester United overcame archrival Manchester City to reach the League Cup final, but was toppled from the English Premier League summit by Chelsea on Wednesday.
Wayne Rooney's 21st goal of the season in stoppage time prevented the Manchester derby going into extra time, and clinched a 3-1 victory at Old Trafford to send United through 4-3 on aggregate.
"There was a lot of spice and at the end there was a special kind of celebration," United manager Alex Ferguson said. "We stayed patient and looked a threat when we stepped it up.
"I thought Wayne Rooney produced a world-class performance tonight, he played better than he did on Saturday when he scored four goals (against Hull). Phenomenal."
United will play Aston Villa in the Feb. 28 final. Big-spending City has not contested a final since 1981.
The focus of the night was on England's second-tier knockout competition, and second-half goals from Paul Scholes and Michael Carrick looked to have clinched a spot in the final for Ferguson's side after overturning the 2-1 first-leg deficit.
Carrick prodded the ball back for Scholes to drive a shot into the net in the 52nd.
And Nani flicked a pass through to Darren Fletcher inside the City box and the midfielder passed to Carrick, who placed his shot in the bottom corner with the aid of the post in the 71st.
But Carlos Tevez volleyed past former United teammate Edwin van der Sar six minutes later to level the semifinal at 3-3 on aggregate.
With away goals not counting until extra time, another 30 minutes was looming until Rooney headed past Shay Given in the second minute of stoppage time.
"We played very well - we were only under pressure for 10 minutes and in those 10 minutes we were very unlucky," City manager Roberto Mancini said.
"But the rest of the game we played very well and I feel very sorry for the players and the fans. I only give compliments to my players, we can go on and win the FA Cup now."
