كتب : Amro Hassan
At Old Trafford, Wayne Rooney and Michael Carrick scored at each half to ensure United the three valuable points.
Second-placed Liverpool earlier lost the chance to keep pressure on United, after the Reds were held to a 4-4 dramatic draw against Arsenal on Tuesday.
Cristiano Ronaldo and Ryan Giggs, who were rested during the Everton FA Cup defeat, were given a starting role against Pompey.
Sir Alex Ferguson opted to deploy Wayne Rooney as a lone striker.
United broke the deadlock on 9 minutes after a pinpoint ball from Anderson released Ryan Giggs on the left flank.
The Welshman squared for the unguarded Rooney to tap in from close range.
It was Rooney's turn to release Giggs in the 31st minute, but the United skipper shot straight at David James.
Five minutes before the interval, Giggs wasted the best chance of the game when he shot wide from Cristiano Ronaldo's cross.
In second half, the hosts were given a couple of nervy moments as Peter Crouch and Glen Johnson wasted two chances for Portsmouth.
However, United retained their grip on the game later on and Rooney could have added a second but James saved the English international's left-footed shot.
The result was put beyond doubt eight minutes from time, when Carrick received Paul Scholes' pass with a cool finish past James.
In another game, Chelsea were held to a goalless draw by Everton at Stamford Bridge.
Everton's highlight of the game was when Tim Cahill went one on one with Petr Cech before the Czech keeper brilliantly saved the Australian's shot.
Didier Drogba was unlucky to see a second-half effort rattle off the cross bar for the game to end in a stalemate.
Watch Rooney's goal
Watch Carrick's goal