It was far from a classic cup encounter, but Wayne Rooney emerged from the bench to save the day with an archetypal striker’s finish and a delicate chip few players are capable of being audacious enough even to attempt.

Portsmouth’s late rally was not enough, although this game should long have been over before Pedro Mendes' strike was deflected in off Nwankwo Kanu in the 87th minute.

United were twice denied goals when they clearly should have stood. First Nemanja Vidic then Henrik Larsson thought they had scored before being overruled by the officials.

Sir Alex made several changes to the team that lost to Arsenal last Sunday. Tomasz Kuszczak, who played against Aston Villa in the third round, came in for Edwin van der Sar, while Rooney dropped to the bench to allow Ole Gunnar Solskjaer to partner Henrik Larsson up front. Cristiano Ronaldo, given time off by the Reds boss, was replaced by Ji-sung Park on the right flank.

United made a slow start to the match without getting into any kind of rhythm in the first ten minutes. Portsmouth had an early shout for a penalty correctly turned down by referee Mike Riley. Andy Cole flicked the ball on for Niko Kranjcar, but he was already tumbling before Kuszczak had even gone to ground to challenge for the ball.

The Reds slowly came into the game when Ryan Giggs expertly pulled back Gary Neville’s lofted long ball forward only to find nobody had anticipated