Portsmouth moved six points clear of the Championship relegation zone as Gustavo Caballero's strike 30 seconds into the second half teed up victory over promotion-chasing Millwall at The Den.

An uneventful first half burst into life when Caballero's powerful strike, after his initial shot was saved, nestled in the back of the net.

The lead was doubled within 10 minutes, with Millenic Alli doing superbly to beat his man down the left flank and find John Swift, who thumped the ball home from the edge of the box.

Millwall, who were chasing a fourth win in five games and had lost just one of their previous 10 matches, pulled a goal back when Casper de Norre found the corner of the net with a delightful curling strike.

But Marlon Pack's instinctive finish made it 3-1 and the visitors held on for a precious win - their second in London in five days, following victory over Charlton on Tuesday.

Although the defeat is a blow to the Lions' automatic promotion hopes, they are only six points behind second-placed Middlesbrough, who could only draw with Oxford, while Ipswich lost to Wrexham.

Pompey edged a tight first half, with Lions keeper Anthony Patterson forced to mark his league debut for the hosts with a fine early save from Caballero, while Ebou Adams wasted two headed chances - one that was well saved and one that he sent off target from close range.

The hosts also missed decent opportunities, and Pompey number one Nicolas Schmid was forced into action on a couple of occasions, notably to keep out a low Femi Azeez shot.

But Pompey upped the tempo in a frantic second half and ended up worthy winners.

Millwall boss Alex Neil:

"I don't think we deserved anything from the game.

"People will think when I say how we defended that I'm talking about the back four, but I'm talking about the whole team.

"This is a collective thing in that the first goal from our point of view was really disappointing and the second goal was equally as disappointing.

"I said to the lads after the game that we're built as a team on doing the basics really well and I didn't think we did the basics well enough.

"When the ball did go forward, it didn't stick enough for us when we got it there and I didn't think we won enough duels."

Portsmouth boss John Mousinho:

"I know we lost to Arsenal [in the FA Cup], but we were excellent on the day and we've replicated those performances away from home.

"I think it's come from a reset after [losing to] Bristol City, and a recognition of the fact that we can do both sides of the game pretty well when we put our minds to it.

"To come here and win, against the third best team in the league - we've watched them time and time again be a very impressive side, home and away from home - is very pleasing.

"They've got threats all over the pitch, so to do that off the back of Tuesday [a win over Charlton] was really pleasing. I thought we were excellent throughout."