Manchester United 3 Manchester City 1: Rooney books Wembley date after sinking City
Last week, in a New York bar named Mad Hatter, City chief executive Garry Cook delivered the best team-talk Sir Alex Ferguson could have wanted as he declared this tie as good as over with the Blues leading 2-1 from the first leg at Eastlands.
Carlos Tevez had threatened to take the semi-final into extra time when he brilliantly turned home Craig Bellamy's cross 14 minutes from time – making the aggregate 3-3 – but up popped Rooney to nod home Ryan Giggs's cross to secure a final with Aston Villa on Sunday, February 28.
Controlling possession against a City side which sat very deep, United had carved out an overall lead thanks to Paul Scholes and Michael Carrick on 52 and 71 minutes respectively.
Only Tevez's refusal to bow at the feet of his old club kept the Blues going, but ultimately it was not enough.
Seven minutes after the restart, and following a brief stoppage after Bellamy had been hit on the back of the head by a coin, Rooney delivered a superb pass for Giggs, who was driven wide by City goalkeeper Shay Given.
The veteran Welshman did not panic and delivered the ball back into the City area and, after, Nani had run into a wall of defenders, Michael Carrick prodded the ball back for Scholes, who drove his shot into the bottom corner.
Twenty minutes later when Nani flicked a superb pass through to Darren Fletcher inside City's box, the Scotland star laid a pass off to Carrick.
The England midfielder is an accurate striker of the ball and his shot was perfectly placed into the bottom corner with the aid of a post.
If Rooney had tapped home Patrice Evra's cross when he was completely unmarked three minutes later, the tie would have been over. Inexplicably, he put it wide.
City made him pay temporarily, Tevez somehow managing to squeeze the ball beyond Edwin van der Sar from the most unlikely angle.
United may have felt aggrieved but Rooney still had one more trick up his sleeve and with it he delivered a very large slice of humble pie for Cook.