Fletcher (right) is congratulated by Rooney after scoring United's winner
Darren Fletcher's deflected first-half strike was enough to give Manchester United victory over Portsmouth.
Pompey went close after only 12 seconds when Papa Bouba Diop's shot whistled past the post, before Wayne Rooney shot straight at David James from 12 yards.
United began to look dangerous down the flanks and from Patrice Evra's cross, Fletcher bundled in via Sol Campbell.
Pompey's best efforts came after the break but Jerome Thomas and Papa Bouba Diop saw their shots saved comfortably.
Portsmouth might have lacked any real cut and thrust but boss Harry Redknapp will take some consolation that their performance was better than the one that saw them thumped 4-0 by Chelsea in their opening game of the season last week.
Redknapp brought in on-loan left-back Armand Traore in a move designed to shore up the defence.
But with United restoring striker Carlos Tevez and Anderson to their line-up, Pompey were always likely to be stretched.
Yet it was the hosts who almost struck first when Bouba Diop rode a challenge before cracking a shot from 15 yards which zipped off the wet turf and was inches wide of the post.
Soon, though, United began to dictate the play, pulling Portsmouth - and particularly Bouba Diop - out of position.
Wayne Rooney made space in the box but hit his shot straight at David James, and shortly after the England keeper kept out a swerving Paul Scholes free-kick.
Jermain Defoe and Peter Crouch were playing their first game together at Fratton Park and they almost combined to get Crouch in, but Evra nicked the ball of the former Liverpool man's toes when he about to shoot.
Back came United and when they worked the ball inside Diop, for the second time in a few minutes, Evra crossed from the left and Fletcher's effort went scrambled in off Campbell as Sylvain Distin failed to hook it off the line.
United might have led 2-0 at the break, but Rooney fired a shot just wide after he had superbly made space with an excellent first touch and turn on the edge of the box.
An hour of the game had been played before Portsmouth forced Edwin van der Sar into his first save, beating away substitute Thomas's vicious drive.
The slicker passing, more incisive movement and more dangerous play continued to come from United after the break, as it had in the opening 45 minutes.
However, the visitors seemed content to sit on their lead as the half wore on and as Pompey crept forward, Van der Sar had to be alert to keep out Bouba Diop's swirling shot.
But with the game compressed into he middle third, and Pompey short of ideas, chances were few and far between.
Despite playing within themselves United always seemed more likely to add to the scoring but Carlos Tevez shot wide from distance and then lofted a free-kick into the arm of James.
The result leaves Portsmouth rooted to the foot of the table, while United move up to fifth.
Portsmouth boss Harry Redknapp:
"I thought I was a very even game up until they scored. The way the first half went, I was well pleased.
"We have three or four players who haven't played for a while and missed a pre-season and I had to throw them in and take a chance on them.
"The work rate was much better today and you couldn't fault the effort. I thought we played okay."
Manchester United manager Sir Alex Ferguson:
"We played some excellent football tonight. This is a difficult place to come, so it is a bonus to come here and win.
"We tried to play a system where the players would be comfortable. We wanted to have Anderson playing centrally, close to Carlos Tevez.
"We let Paul Scholes control the game, and used Darren Fetcher's energy."
Man Utd: Van der Sar, Brown, Ferdinand, Vidic, O'Shea, Fletcher, Anderson (Possebon 76), Scholes, Evra, Rooney, Tevez.
Subs Not Used: Kuszczak, Neville, Fabio Da Silva, Rafael Da Silva, Gibson, Campbell.
Booked: Brown, Fletcher.
Goals: Fletcher 32.
Ref: Chris Foy (Merseyside).
BBC Sport Player Rater man of the match: Man Utd's Darren Fletcher 7.09 (on 90 minutes).
• Please note that you can still give the players marks out of 10 on BBC Sport's Player Rater after the match has finished.
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