Swansea City suffered their first home defeat of the season as a late Burnley goal gave the visitors the three points at Landore in the Professional Development League.
Tom Tweedy grabbed the winner to condemn the young Swans to a league defeat in SA1 for the first time since November 2022.
The Clarets had taken the lead in the first half through Tommy McDermott’s penalty, before Kyrell Wilson responded with a smart finish for the home side after the break.
But a late goal from ex-Swan Tweedy settled the contest, and put a dent in the Swans play-off ambitions.
Coach Anthony Wright had made three changes from Saturday’s win against Bristol City with Kit Margetson, Charlie Veevers and Glory Nzingo coming into the starting 11.
The Swans started brightly, with the first chance falling to midfielder Joel Cotterill, whose low strike from distance was parried away by Charlie Casper.
The ball soon came the way of Veevers in the box, however his close-range effort flew over the crossbar.
But it was the visitors who got the breakthrough, McDermott scoring from the spot after Kit Margetson had fouled a trialist in the box.
Swansea responded well to the setback, and nearly grabbed an equaliser when Wilson took a ball down on his chest to play Nzingo in on goal, but Casper was equal to the forward’s shot.
The hosts kept pressing, Ben Lloyd unable to connect with a Maliq Cadogan cross, before the latter saw two shots blocked just before the interval.
Swansea continued to apply pressure after the restart, and got their reward when sharp link-up play between Cotterill and Lloyd set up Wilson, who took a touch before dispatching a powerful effort beyond Casper to level the scores.
Cameron Congreve drifted a curling strike wide, while Wilson was denied by a good save from the Burnley keeper.
At the other end, Lewis Richardson drove into the box and sent a shot over the bar, and then dragged another effort wide.
Chances kept coming. Nzingo being denied from close-ranged, while Richardson scuffed an effort wide.
But the Clarets would snatch the lead just before the 90-minute mark when Tweedy produced a fine finish.
Swansea City U21s: Kit Margetson, Joe Thomas (Iestyn Jones 60), Kian Jenkins, Joel Cotterill, Filip Lissah, Charlie Veevers, Kyrell Wilson, Glory Nzingo, Maliq Cadogan, Ben Lloyd, Cameron Congreve.
Unused substitutes: Sammy Henia-Kamau, Evan Watts, Josh Carey.
Burnley U21s: Charlie Casper, Alex Healy-Byrne, Ollie Pimlott, Benn Ward, Murray Campbell, Will Hugill, Vernon Masara (Bradley Grant 92), Tommy McDermott (Lewis Richardson 45), Joe Bevan (Basilio Socoliche 77), Trialist (Trialist 62), Tom Tweedy.
Unused substitutes: Felix Chester.