Arsenal rested most of their big guns in view of the important mid-week match but still proved to be too good for Portsmouth and costed to victory.
Arsene Wenger made eight changes from the starting XI at Old Trafford, with the likes of captain Cesc Fabregas, Togo striker Emmanuel Adebayor and regular goalkeeper Manuel Almunia all rested.
However, the young Gunners, skippered by Andrey Arshavin who cannot play in Europe, again showed their potential as a brace from Nicklas Bendtner – his first after a blunder from England keeper David James – and a clinical second-half strike by Mexican Carlos Vela sealed a comfortable victory.
Arsenal need their top players healthy for the showdown with Manchester United. United lead 1-0 after the first leg held at Old Trafford.