Manchester United kept up the pressure at the top of the Premier League as they romped to victory over a woeful Portsmouth at Old Trafford.

The struggling south-coast club never looked like troubling the champions and were put to the sword by Sir Alex Ferguson’s side.

United dominated the opening stages but failed to make their superiority count with Johnny Evans heading their best chance wide.

Dimitar Berbatov should have put the home side into the lead after good link up play from Antonio Valencia and Gary Neville. However, the Bulgarian international shot wide from six yards out.

Rooney made no mistake soon after though, heading Darren Fletcher’s cross from the right past David James, to claim his 23rd goal of the season.

Nani then forced a second for United before half-time when he attempted to put a cross into the box from the left which deflected off Anthony vanden Borre and trickled past James as he dived in the opposite direction.

Michael Carrick claimed United’s third, hitting a fine shot from 25 yards which went in off the underside of the bar, before Berbatov made it 4-0 with a shot from outside the area that found the bottom corner.

Marc Wilson then scored Portsmouth’s second own-goal of the game, firing an attempted clearance into the top corner to give United a comfortable win and round off a miserable afternoon for Avram Grant's side.