With big matches looming, Liverpool manager Rafael Benitez rested Gerrard and didn't not send him into the fray until the 67th minute, as a replacement for Igor Biscan.
Liverpool picked up three useful points in their quest for automatic entry to next years Champions League, while for Portsmouth defeat means they still have some work to do to avoid being sucked again into relegation trouble.
The Reds should have been ahead after only three minutes, Milan Baros was denied by the legs of home goalkeeper Jamie Ashdown.
It was the first of many outstanding saves by the young Portsmouth keeper although he might have been at fault for Liverpool opener after four minutes.
John Arne Riise crossed from the right and although Ashdown blocked the first shot from Fernando Morientes, the keeper could not hold the effort and the grounded Morientes scuffed in the rebound.
Morientes missed an easy headed chance after 25 minutes before Portsmouth levelled eight minutes later.
Liverpool had every player in the penalty area, but they were unable to defend the corner on the right by Gary O'Neil and Diomansy Kamara forced the ball over the line.
Riise missed enough opportunities to have claimed a hat-trick but Liverpool were ahead in the last minute before the break.
The Norwegian was the creator again with a centre from the left which was headed home powerfully by Luis Garcia.
Ashdown was Portsmouth's saviour in the second half with two saves from Riise and two from man of the match Xabi Alonso.
Pompey's best chance fell to former Liverpool star Patrik Berger, whose powerful left-foot shot from 30 yards stretched Jerzy Dudek into his only meaningful action of the second half.