A Steven Gerrard penalty after a handball in the area gave the Reds the lead after 36 minutes in what was a tightly contested cup tie. The goal was Gerrard's 17th of an impressive season.
It was 2-0 four minutes later when John Arne Riise, playing in midfield instead of the rested Harry Kewell, scored his second of the season from the edge of the 18 yard box.
The Reds were comfortably in charge at the break but a goal from Sean Davis after 54 minutes brought the tie to life again. However, despite giving their all in the search for an equaliser, Portsmouth didn't really threaten Reina's goal and Liverpool were able to see off Pompey without having to raise their game.