Diaby produced one of his best performances for Arsenal
Arsenal continued their impressive start to the season with a resounding victory over struggling Portsmouth.
Abou Diaby opened the scoring with a first-time finish from Eduardo's cut-back and doubled the lead when he tapped in Emmanuel Eboue's cross.
Younes Kaboul headed in to give Portsmouth hope but Arsenal responded when the ball rebounded off William Gallas's face and into the net.
Aaron Ramsey slotted home a Robin van Persie pass to seal the hosts' win.
The result sends Arsenal top of the league on goal difference and maintains their 100% start to the season in all competitions.
But with their Champions League qualifying play-off second leg against Celtic on Wednesday and a trip to Manchester United on Saturday, manager Arsene Wenger will be sweating on the fitness of captain Cesc Fabregas, who went off at half-time with a hamstring injury.
Portsmouth drop to the foot of the table and, despite engineering a number of clear-cut chances, look to be in desperate need of reinforcements.
With three defeats from as many games, the south coast club have now made their worst start to a Premier League season and they can only hope that the ongoing saga surrounding their ownership is resolved soon.
They have not won away from home since beating Sunderland on 8 November 2008 and the departures of Glen Johnson, Sean Davis and Peter Crouch have left them looking listless in defence, midfield and attack.
To compound their woes, goalkeeper David James was forced off with an injury to his left knee, a sight which would not have pleased on-looking England coach Fabio Capello ahead of his side's World Cup qualifier against Croatia on 9 September.
On a brighter note, loan signing Frederic Piquionne looked dangerous throughout and the 30-year-old French forward could prove a key addition to a squad that might well be heading for a relegation battle.
Wenger made four alterations to his starting line-up - Eboue, Kieran Gibbs, Diaby and Eduardo replacing Bacary Sagna, Gael Clichy, Alexandre Song and Nicklas Bendtner - but the change of personnel did little to disrupt a rhythm that had brought Arsenal impressive wins against Everton and Celtic.
Wenger enjoys Arsenal victory
A neat passing move between Denilson and Fabregas sent Diaby bearing down on goal but the Frenchman seemed to get caught in two minds and was eventually thwarted by Nadir Belhadj.
Visiting full-backs Belhadj and Marc Wilson were enduring a torrid afternoon and when Eduardo skipped past Wilson on the left, the Croatian was able to square for Diaby to crash a side-footed finish into James's top left-hand corner.
Arsenal were purring and four minutes later they doubled their lead - Fabregas playing Eboue in behind Belhadj and the Ivorian crossing for Diaby to roll the ball past James from close range.
The hosts squandered numerous chances to extend their advantage and their profligacy allowed Portsmouth to grow in confidence.
Their first clear-cut opening of the first half saw Kanu sashay in off the right wing and tee up John Utaka, only for Eboue to arrive with a last-ditch block.
Score did not reflect game - Hart
Paul Hart's men were working hard to force a way back into the match and they were rewarded when Kaboul towered above a static Almunia to nod in Belhadj's centre from the left.
Pompey continued to press forward at the beginning of the second half and picked holes in the Arsenal defence on a number of occasions, but their hopes of completing a comeback were soon dashed.
An Andrey Arshavin free-kick from the left was headed on by Van Persie and knocked across goal by Thomas Vermaelen, before it hit Gallas in the face and went in via a post.
Portsmouth almost responded through Piquionne, the France international surging through on goal but delaying his shot long enough for Gibbs to get back, while Utaka fired wide from a glorious position late on.
But by that point 18-year-old Ramsey had put the game to bed with his first league goal for Arsenal, an assured finish having collected Van Persie's slide-rule pass.
Arsenal manager Arsene Wenger: "We have had a brilliant start. It should create confidence and momentum.
"We now go into another week which will be another test against Celtic and then Manchester United. It looks to be exciting and interesting.
"We want to make this place very special, and there is still some more work to do. However, you also have to accept the team have to get the people off their seats, not the other way around.
"Last year maybe we did not give enough belief to our fans, and maybe the belief of our fans had been affected by the negative publicity we got."
Portsmouth manager Paul Hart: "We can dwell on bad things, bemoan our luck, or you can dust yourself down and get on with it.
"There is no point moping around and feeling sorry. You can get on with it or walk away. I work for a good football club, with good people, but one which is just having a bad time.
"There has been no problem from the application in the players. While we have this kind of spirit, we can make progress."
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