Jason Roberts climbed off the bench to hit a late double as Blackburn came from behind to claim three priceless Barclays Premier League points with a 3-1 win over fellow strugglers Portsmouth.

Jamie O'Hara had put Pompey in front with a 30-yard effort in the 15th minute, but things changed after Sam Allardyce rang the changes at the break.

Roberts steered home a 52nd-minute equaliser, before Ryan Nelsen headed Rovers in front with a rare strike in the 73rd minute. Roberts then wrapped up the points with five minutes to go.

Rovers started best in their bid to exit the drop zone, a Pascal Chimbonda shot causing chaos in the Pompey box and almost presenting a chance for El-Hadji Diouf.

Younes Kaboul and O'Hara's low shots dribbled wide for the visitors while Anthony Vanden Borre messed up a half-chance after being fed in the box by Kevin Prince-Boateng.

Pompey's lead came out of nowhere when Aruna Dindane fed O'Hara and he found a way past Paul Robinson with a low shot from 30 yards.

Rovers' woes were summed up in the 33rd minute when, having won a free-kick 30 yards from goal, the recalled Morten Gamst Pedersen lofted a pitiful set-piece attempt high and wide.

After boos greeted the end of a dismal first period, manager Allardyce had no choice but to make changes, introducing Roberts and Benni McCarthy in place of Diouf and Pedersen. But Pompey came close to grabbing a second in the 50th minute when O'Hara curled in a free-kick from the left and Kaboul rose to glance his header just wide.

Allardyce's double change paid dividends when Nelsen headed down David Dunn's corner in the box and Roberts reacted quickest to steer the equaliser past David James.

Nelsen's superb 73rd-minute header put the home side in front and Roberts wrapped up the points five minutes from time.