Swansea City missed the chance to return to the top of the Championship as they slumped to a 3-1 defeat by Portsmouth in a remarkable game at Fratton Park.

Terry Devlin guided home from 10 yards to give Pompey a deserved lead late in the first half and John Mousinho's team seemed for a long time like holding on for a 1-0 win.

Swansea then appeared to have snatched a point when substitute Zan Vipotnik coolly converted from the penalty spot five minutes from time after Regan Poole tugged the Slovenia striker's shirt.

Vitor Matos' team should then have gone ahead three minutes later when Ross Stewart shot against the bar, but it was Portsmouth who struck again when full-back Devlin drilled home from a half-cleared corner in the second minute of added time.

With Swansea throwing players forward in search of a second equaliser, Thomas Waddingham latched on to a long ball forward and got the better of Ben Cabango before steering in Portsmouth's third in the 98th minute.

That made certain of a third defeat in four matches for Matos' early-season pacesetters, who have lost momentum after their fine start to the campaign.

While Swansea drop out of the Championship's automatic promotion places and into fourth, Portsmouth climb to 10th – and are only outside the play-off spots on goal difference – after extending their unbeaten run to six games.

After beginning this season with defeats in three of their first four league games, Portsmouth have turned heads with a spectacular upturn in form which has seen them lose only one of their past 10.

They looked hungry to claim their most notable result yet against a Swansea side who were given a taste of their own medicine as they struggled in the face of a high press.

Pompey had chances before Devlin beat the dive of Lawrence Vigouroux to open the scoring after Swansea had lost possession in their own half.

Swansea, by contrast, were short of their best going forward throughout, yet they may well have snatched victory from the jaws of defeat had Stewart not turned Josh Key's inviting centre on to the woodwork.

Instead, Portsmouth found a way to win during a thrilling climax before players and staff from both clubs were involved in a melee after the final whistle.

While the home contingent were left to celebrate when calm was restored, frustration reigned for Swansea.

Portsmouth head coach John Mousinho:

"A massive win and a rally important night for us for a lot of reasons.

"I thought we were excellent in the first half. I thought we were really diligent in the way we defended and broke forward a couple of times.

"Second half we started well and probably tired a bit. I was disappointed with the way we conceded the penalty.

"But to respond to the equaliser like we did was absolutely magnificent."

Swansea head coach Vitor Matos:

"It was a game that we expect, a lot of physicality, a lot of second balls, a lot of duels, a lot of verticality.

"That's how it was in the first half. We concede in one of those situations.

"Then step by step we started to bring the game back to us. I think we did really well after half-time. We scored and then the game could have come to us.

"In the end it went to Portsmouth from a corner, so that's something we need to do better. It ended 3-1 but that was a situation where we were really pushing to try to get a point."