Peterborough launched what had looked an unlikely comeback as Sammie Szmodics swept in and Jack Marriott scored just seconds after coming off the bench.

But Obafemi levelled with a crisp volley before Piroe steered in his 17th goal of the season to deny Posh a draw.

Defeat means Peterborough are seven points adrift of safety with nine games remaining.

Their winless league run now stands at 15 games, with Grant McCann still looking for a first triumph since taking charge of the club for a second time last month.

Swansea climb to 15th having bounced back from successive defeats with a fifth away league win of the campaign.

There were doubts around an hour before kick-off over whether the game would go ahead because of heavy rain in Cambridgeshire, but referee Oliver Langford deemed the surface playable and the tricky conditions did not appear to trouble Swansea during a dominant first-half display.

Russell Martin's team took control from the outset, with Peterborough seemingly content to sit deep and hope to strike on the counter.

Obafemi threatened first, forcing a decent save from David Cornell and then lifting over the bar as he stretched to meet Joel Piroe's centre.

Piroe then curled goalwards from 20 yards only for Cornell to push the ball around the post.

Peterborough looked like a team who had not won a league match since 11 December, and the goal Swansea's near total control merited eventually came when Jamie Paterson's pass found Obafemi and he beat Cornell despite the angle being against him.

The hosts had no choice but to take a bolder approach after the break - and a willingness to commit more players forward brought almost immediate reward.

Played into space down the left, Ricky-Jade Jones' pace took him beyond Cyrus Christie and a perfect cross teed up Szmodics for a first-time finish which left Swansea goalkeeper Andy Fisher with no chance.

Sammie Szmodics runs away to celebrate after scoring his fourth goal of the season

Swansea ought to have retaken the lead when Paterson fed Hannes Wolf in space in the box, but Cornell came off his line to deny the Austrian a first goal in English football.

Peterborough suffered a blow when Jones, who had been their best player, was forced off with what looked like a shoulder injury.

Yet remarkably, his replacement scored within seconds of entering the field.

Having got themselves into trouble, Swansea still should have escaped when Kyle Naughton picked up possession in his own box, but his mishit clearance presented Marriott with his first touch.

The striker accepted the gift, rolling a shot inside the far post to put Peterborough ahead.

Now it was Swansea's turn to conjure a response, with Obafemi finishing sharply on the rebound after Christie had headed Paterson's deep cross against the post.

Cornell then pawed out Christie's low drive, but the one-time Swansea goalkeeper could do nothing to save Peterborough as Olivier Ntcham's blocked shot fell to Piroe and the Dutchman stroked home from 15 yards.

Peterborough manager Grant McCann:

"The first half we didn't get against the ball enough. We let Swansea dictate most of the first half. We knew exactly what they were going to do but we didn't get the press right.

"We sat too defensive in our shape, we didn't jump to the ball. We end up almost like a flat seven or eight at times at the beck. At times like that you need a bit of organisation, you need people to push people on.

"Second half we reshuffled a bit, got ourselves back into the game, played a bit more on the front foot and took the lead through Jack.

"Then you are hoping we can manage the game. I felt we sat back in our shape again. Maybe it's a confidence, maybe it's know-how, maybe it's a little bit of game management that we probably lack. That probably showed."

Swansea head coach Russell Martin:

"I am still trying to digest the first 15 minutes of the second half, which I am really disappointed with. I cant believe the game turned into that to be honest. But the players showed real courage to finally get control back. We deserved to win - we should be out of sight at half-time.

"I will continue to be proud of this group for what they are showing but for 15 minutes there - when the first half was so good, so dominant - we were nowhere near.

"That's why we are where we are in the league. On our day we are capable of producing some incredible moments, some brilliant football. But the gap between when we are really good and when we are not is too big. You saw that in one game today.

"I have chosen not to speak [in the dressing room] tonight. I said well done for showing some courage but we'll talk about it on Friday and we'll learn and dissect the game."