Cristiano Ronaldo's stunning double in the space of three minutes was the highlight as Manchester United returned to the top of the Premier League table.
Ronaldo, with 27 goals, has already bettered his tally from last season
With the influential Paul Scholes back, the champions ran riot early on and Ronaldo put them ahead after a slick one-two with Nani on nine minutes.
Moments later the Portuguese winger lashed a 30-yard free-kick into David James' top corner in typical fashion.
Though they battled bravely throughout, the scoreline flattered Pompey.
The visitors, with seven wins on the road this season, went for a typically adventurous 4-4-2 formation with Milan Baros making his debut but Harry Redknapp's bravery immediately backfired.
With the 33-year-old Scholes making his first start since October, United put Pompey under intense early pressure.
Nemanja Vidic, back to partner Rio Ferdinand in defence, lofted a clever ball over the top of Pompey's defence for Park Ji-Sung but Sol Campbell recovered to clear the danger.
But Ronaldo, given a central striking role alongside Wayne Rooney, quickly put United two goals up in stunning fashion.
Firstly, on nine minutes, Scholes played an instinctive first-time pass to the reigning PFA Player of the Year who chested down and then raced away to collect Nani's perfectly weighted pass in the penalty area.
With just James to beat, Ronaldo opened up his body and coolly slipped the ball through the Portsmouth keeper's legs.
Three minutes later the Portuguese winger drew gasps of disbelief from the Old Trafford crowd with another display of his unique gifts.
Lining up a free-kick from 30 yards, Ronaldo lashed the ball with incredible pace and power into the very top corner.
Ronaldo lashed home his second from a free-kick in distinctive style
Shell-shocked, Portsmouth fought to get back into the game and Baros should have collected Lassana Diarra's clever through-ball after slipping through United's defence unnoticed.
But with French full-back Patrice Evra marauding down the left, and Scholes pulling the strings, United were dominant.
England striker Rooney should have extended their lead but swiped at the ball carelessly when presented with a clear chance from six yards out after Scholes, Nani, and then Evra, had all linked well to play him in.
Pompey boss Redknapp rang the changes at half-time bringing on Hermann Hreidarsson for Sylvain Distin and Arnold Mvuemba for Lauren.
Though his tactical ploy succeeded in making the game scrappier, United still carved out chances.
James, making his 500th Premier League appearance, saved well from a powerful Ferdinand header on 50 minutes and Rooney, looking out of sorts, fluffed an attempted lob from 20 yards with only the veteran Pompey stopper to beat.
Portsmouth did manage to build some passages of possession, mainly through Diarra, Baros, and the impressive Niko Kranjcar.
But when United stole the ball they were incisive, with Rooney and Ronaldo forcing Campbell into a number of last-ditch clearances.
United's forward pairing were brought off with 15 minutes to go and, with Owen Hargreaves coming on to shore up the midfield, the home side continued to go close as they secured a victory which took them back to the top of the table.
Manchester United manager Sir Alex Ferguson:
"David Beckham's strike rate was pretty good, Eric Cantona used to take them too but Ronaldo's strike rate is phenomenal.
"That without doubt must be the best (I've seen in the Premier League). From that distance he is going to hit them. No keeper in the world would save that.
"The boy practises. It's a delight to see, terrific."
"I think it was a fantastic performance - one of the best this season. I can't believe it was only two. We missed a few chances, but at the end of the day you've got to think about the performance."
Portsmouth assistant manager Tony Adams:
"United were exceptional, especially in the first 45 minutes. From our point of view, we didn't play that well and we didn't keep the ball.
"We didn't turn up in the first half but we did get into them more in the second half.
"Their substitutes bench is phenomenal and it's a difficult place to come when you're not playing well yourselves.
"Our players will grow and they will learn from this. We need to get back on track because we have a tough game against Chelsea at the weekend."
Man Utd: Van der Sar, Brown, Ferdinand, Vidic, Evra, Nani, Scholes (Anderson 62), Carrick, Park, Ronaldo (Hargreaves 73), Rooney (Tevez 73).
Subs Not Used: Kuszczak, O'Shea.
Goals: Ronaldo 10, 13.
Portsmouth: James, Johnson, Campbell, Distin (Hreidarsson 46), Pamarot, Lauren (Mvuemba 46), Davis, Diarra, Kranjcar, Baros (Hughes 78), Mwaruwari.
Subs Not Used: Begovic, Pedro Mendes.
Ref: Martin Atkinson (W Yorkshire).
BBC Sport Player Rater man of the match: Manchester United's Cristiano Ronaldo 8.94 (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.