Arsenal booked their place in next season's Champions League with a win that means Portsmouth are still yet to secure their Premier League status.
Pompey goalkeeper David James gifted Arsenal the opener when he fumbled Nicklas Bendtner's header into his net.
The Dane then grabbed a second from the penalty spot after Sean Davis was ruled to have fouled captain Andrey Arshavin.
Carlos Vela lashed home a third before Noe Pamarot was sent off for bringing Arshavin down when through on goal.
Arsenal's victory moves them 13 points clear of fifth-place Aston Villa, who play on Monday, and they are now mathematically guaranteed to finish at least fourth.
They are unbeaten in 21 league matches and have scored at least three goals in each of their last five away league games, equalling a club record set in 1932.
Portsmouth are seven points clear of the relegation zone but need another six from the remaining nine available to make absolutely sure of their survival.
Their run without a victory over one of the 'big four' extends to 17 games but they will be confident of avoiding the drop, with Blackburn, Sunderland and Wigan their final three opponents.
Gunners boss Arsene Wenger clearly had an eye on his side's Champions League semi-final second leg against Manchester United on Tuesday, and made eight changes to the XI that started the first leg at Old Trafford in midweek.
Portsmouth manager Paul Hart:
"The boys are adamant that it was not a penalty for their second goal and I agree with them. There was no physical contact."
"I am not here to vilify referees. We have had a few decisions go against us recently but it is a tough life for referees and it is for us."
"Everyone around us in the table has lost today, so there is no change. We just have to look after ourselves."
Arsenal manager Arsene Wenger:
"I wanted to give a breather to some of the players ."
"I have no doubts about the younger players because I see them every day and what we work on, you could see that on the pitch today."
"We were sharp, composed and mobile with a great attitude."
Portsmouth: James, Pamarot, Campbell, Distin, Hreidarsson (Kanu 46), Pennant (Utaka 46), Davis, Hughes, Mullins, Belhadj, Crouch.
Subs Not Used: Begovic, Primus, Nugent, Basinas, Cranie.
Sent Off: Pamarot (78).
Booked: Campbell, Kanu, Davis.
Arsenal: Fabianski, Sagna, Song Billong, Djourou, Eboue, Walcott (Bischoff 64), Denilson, Ramsey (Randall 82), Arshavin, Bendtner (Merida 77), Vela.
Subs Not Used: Mannone, Coquelin, Emmanuel-Thomas, Frimpong.
Booked: Arshavin.
Goals: Bendtner 13, 41 pen, Vela 56.
Att: 20,418
Ref: Lee Mason (Lancashire).
www.bbc.co.uk
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Valenciennes FC 2 - 0 Olympique Lyonnais
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Starting the game in the north four points behind second-placed Bordeaux and a further two adrift of leaders Marseille, Claude Puel's side knew they had to leave the Stade Nungesser with a victory to maintain realistic hopes of catching the front pair.
However, without captain Juninho, who looks set to leave the club this summer, Lyon looked short of inspiration and resigned to not winning the championship for the first time in eight seasons.
The hosts seized the initiative with a two-goal burst in the space of six first-half minutes.
Deputising for the injured Jean-Claude Darcheville, Johan Audel stole the show, first outpacing Jean-Alain Boumsong to opening the scoring on 23 minutes before squeezing between François Clerc and Cris to add number two soon after.
It must have been particularly galling - if not surprising - for Puel, who had nutured Audel's fledgling talents at Lille.
The 25-year-old's double strike means Valenciennes are all but assured of top-flight football next season.
Lyon, who were reassured by club president Jean-Michel Aulas this week that a fourth-place finish would not be a financial catastrophe, will be watching Paris Saint-Germain's match with Rennes on Sunday with a vested interest.
www.ligue1.com
