An injury-time goal from Rory Donnelly ensured that a well-deserved point slipped out of the development side's fingers as Swansea picked up a 2-1 victory at Tooting and Mitcham FC.
A fine individual display by Sullay Kaikai was capped off with a goal three minutes from time which looked to have grabbed a share of the spoils for the Eagles but Gary Issott's men were hit with a sucker punch with one of the final kicks of the game.
The first half was a drab affair with not many chances for either side, but Kaikai ratttled the bar with a trademark free-kick just six minutes in after a foul on Kyle de Silva.
Not long after Swansea carved out a great chance to take the lead when a neat one-two between Kenji Gorre and Kris Scott saw the former deliver a great ball into the feet of Donnelly, but despite being well positioned the striker blasted wide of the target.
The rest of the first-half saw little goalmouth action with only a speculative try from Ibra Sekajja when Gregor Zabaret was out of position in the Swans goal which ended up in the goalkeeper's arms and another Kaikai dead ball missing the target the only real chances of a quiet half.
The second 45 started in a brighter vain, with Kaikai heading narrowly off target after meeting a Luke Croll cross seven minutes after the restart, and soon after Gary Issot's men almost forced an own goal when Ibra Sekajja sped down the right and centred for Alex Wynter whose mis-cued shot hit Jernade Meade and just trickled past the post.
However one lapse in concentration cost Palace dear after 67 minutes. After a throw-in had been conceded the Eagles switched off and allowed Henry Jones to advance to the byline and cut the ball back for Scott who easily converted from six yards to snatch the lead.
The hosts were working hard to pull themselves level again and Derek Tieku glanced a header wide after good work by Conor Dymond and seconds after coming on Hiram Boateng sprinted into the area and drove at goal but was left frustrated by Zabaret.
But with three minutes to go the Eagles grabbed a deserved equaliser when Jerome Williams got down the left flank and played in Boateng who put the ball on a plate for Kaikai to steer home a deserved goal for both the winger and his side.
But with a minute to play Scott found himself in space on the left and hit a low centre which found its way to Donnelly who side-footed the ball past Neil Alexander, and despite the keeper getting a hand on it the ball nestled in the back of the net to deliver a cruel blow to a young Eagles side.
Palace: Alexander, Taylor, Williams, Dymond (Boateng 84), Inniss, Chambers, Kaikai, Wynter, Sekajja, N. Guedioura (Tieku 51), De Silva (Croll 19). Subs: Fitzsimons, Udumaga
Swansea: Zabaret, Shephard, Meade, Jones, Alfei, Tancock, Bray, Lucas, Scott, Donnerly, Gorre (Laveridge 77). Subs: Davies, Gogic, Hedges, Davies