Nottingham Forest struck late on to come from behind and condemn the Swans to a fourth consecutive defeat.
The Swans had looked on course for victory when George Byers’ volley deflected in off Connor Roberts with 14 minutes left.
But two goals from two corners sunk the Swans at the City Ground in a game which was in their hands for large parts.
Sub Daryl Murphy put Forest back on level terms four minutes later as the hosts reacted quickly to falling behind.
Then, with two minutes left, Molla Wague headed in another corner to keep Forest’s play-off bid on track.
Defeat leaves the Swans on 47 points from 37 games with Graham Potter’s side in 15th place.
McBurnie returned to the starting line-up after the Scotland international - Swansea's top scorer this season - missed the defeats to Norwich, West Brom and Manchester City through illness.
Wayne Routledge was missing after his wife gave birth to a baby boy on Friday while the other alteration saw Kyle Naughton back in the Swans defence after a groin issue. He started at left-back as Matt Grimes moves into midfield and Jay Fulton drops to the bench.
Kristoffer Nordfeldt continued in goal - with Steven Benda on the bench after Erwin Mulder was ruled out for the rest of the season with a broken finger - with Naughton joining Connor Roberts, Mike van der Hoorn and Cameron Carter-Vickers in front of the Swedish international.
Grimes joined Byers and Bersant Celina in midfield, with Daniel James and Nathan Dyer operating on the flanks with McBurnie in the central striker role.
The Swans started brightly with the lively James being denied twice with blocked shots.
Grimes saw an effort deflected wide while, at the other end, Jack Colback drove a low strike wide.
From then on it was the Swans who looked the more likely to break the deadlock, with Celina latching on to van der Hoorn’s scooped pass but the Kosovan couldn’t control it in time as keeper Costel Pantilimon gathered.
Referee Jeremey Simpson then booked McBurnie for simulation in the box as the Scot tumbled under a challenge with the Swans appealing for a penalty.
Before the break, Grimes was denied by a superb save from Pantilimon as he kept out the midfielder’s stunning 30-yard drive.
Potter’s side continued to plug away and they looked the brighter team again in the second half.
Another surging run from van der Hoorn saw the Dutch defender race 30 yards before sending in McBurnie, but he curled his effort wide from inside the box.
The chances kept coming, and Byers was only denied by the stretching hand of Pantilimon as his bouncing header looked destined for the net.
The Forest stopper again came to the hosts’ rescue as he kept out Celina’s free-kick, before the Swans deservedly got their goal.
Fine work by Celina down the left ended with his cross meeting Byers, and his volley deflected off Roberts and into the net.
But the cheers had barely died down by the time sub Murphy made the most of his physical presence to nod in the equaliser from a corner.
Then, with two minutes left, an almost replica goal saw Wague climb highest to head in past Nordfeldt in a crowded box.
It was a bitter pill to swallow, and it was a sixth consecutive defeat on their travels.
Nottingham Forest: Costel Pantilimon, Jack Colback, Lewis Grabban (Daryl Murphy, 66), Ben Watson (capt, Joao Carvalho, 66), Ben Osborn, Molla Wague, Matty Cash, Ryan Yates (Pele, 57), Joe Lolley, Tendayi Darikwa, Yohan Benalouane.
Subs: Luke Steele, Jack Robinson, Claudio Yacob, Karim Ansarifard.
Swansea City: Kristoffer Nordfeldt; Connor Roberts, Mike van der Hoorn (capt), Cameron Carter-Vickers, Kyle Naughton; George Byers (Courtney Baker-Richardson, 84) Bersant Celina, Matt Grimes; Nathan Dyer (Barrie McKay, 70), Oli McBurnie, Daniel James.
Subs: Steven Benda, Cian Harries, Declan John, Jay Fulton, Joel Asoro.
Attendance: 28,469
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30th March