Liverpool booked their place in the last 16 of the FA Cup after a 2-1 win over Portsmouth at Fratton Park, but they were made to work by their hosts and looked anything but the stable outfit of late.

The Reds were cruising at half-time after Steven Gerrard converted a 37th-minute penalty - awarded following a handball by Dejan Stefanovic - before John Arne Riise doubled the advantage four minutes later.

But Sean Davis headed in Gary O'Neil's free-kick nine minutes into the second half to rejuvenate Harry Redknapp's side, although the south coast side were unable to find an equaliser.

Lone-striker Vincent Pericard, working tirelessly against both Jamie Carragher and Sami Hyypia, ensured Portsmouth were just as dangerous in front of goal as their visitors.

Stephen Warnock worked hard to turn a dangerous Gary O'Neil cross over his own bar and in the 27th minute Pedro Mendes tested Jose Reina with a well-struck half-volley.

Pompey's five-man midfield had plenty of possession and when Liverpool tried to get through on the flanks the home team's full-backs looked sound.

Linvoy Primus, playing his first game since Boxing Day after a groin injury, floored Gerrard with with a thumping shoulder-charge, which the Liverpool man calmly accepted.

And Pericard, Richard Hughes - who scored a fifth-round Pompey winner against Liverpool two years ago - and Sean Davis were all booked while former Red Gregory Vignal was lucky to escape punishment for an elbow on Gerrard.

But Liverpool were handed a goal out of the blue in the 36th minute when Gerrard's corner took a bad bounce and hit Stefanovic on the arm as he and Primus both tried to clear the same ball.

Despite the jeers of the home crowd, Dowd appeared to have no alternative but to award a spot-kick and Gerrard stepped up confidently to score his 16th of the season.

Four minutes later it was 2-0, thanks to a fine finish by Riise. When Fernando Morientes' flick sent him racing down the left he held off Primus' challenge and powered a low drive past debut-making Dean Kiely.

And it would have been three but for Kiely's brave advance and save at Morientes' feet after a dreadful error by Vignal.

In the face of a potential hammering again, manager Harry Redknapp risked a second striker in the second half despite last week's 5-0 thumping at Birmingham. And it was only justice that he received some sort of reward for his optimistic ambition.

There were still 35 minutes left on the clock when Sean Davis' first goal since signing from Spurs earlier this month threatened to turn the tie.

When Gary O'Neil was fouled he curled in a free-kick and Davis' back-header slipped away from the diving Jose Reina.

Liverpool lost to Burnley in the third round last year and Pompey the year before. They had to come back from 3-1 behind to beat Luton last time out.

But here they just settled for a narrow victory and somehow escaped some shaky defending.

By the end they had all three substitutes, Peter Crouch, Harry Kewell and Steve Finnan on the pitch, defying a gung-ho series of Portsmouth corners.

Stefanovic just cleared the bar with a 30-yard free-kick, Reina twice fell on the ball in nightmare goalmouth collisions and somehow they survived.