Palace's development side were the victims of a second-half rally by Cardiff City who turned around a half-time deficit to pick up a 2-1 victory at Tooting and Mitcham's KNK Stadium.
Connor Dymond's well-taken penalty had given Gary Issott's men the advantage but the Welsh side recovered to collect all three points, with the positive for Palace being Jonny Parr and Paddy McCarthy collecting useful minutes in their quest a first-team return.
The first chance fell to City when former Birmingham City man Jordan Mutch slipped in Kadeem Harris but his low strike was straight at Alexander.
However the visitors came much closer to breaking the deadlock when Tommy O'Sullivan picked the ball up in midfield and unleashed a rocket of a shot that thumped against the crossbar from 30 yards as the visitors enjoyed the better opening.
Palace's first chance fell to Ibra Sekajja but the striker couldn't trouble Simon Moore in the Bluebirds' goal with a shot under pressure, but Kyle De Silva fired wide from just outside the area as the Eagles began to get a foothold in the game.
But just before half-time they were given a chance to convert from the penalty spot when after a shot from Elliot Grandin was saved by Moore's leg, Sullay Kaikai was tripped in the area. Dymond made no mistake from 12 yards as he sent the keeper the wrong way to hand his side the lead at half-time.
Parr came off at the break having amassed a useful 45 minutes of game time but four minutes after the restart the referee was pointing to the spot again when Mutch was bundled over in the box by Quade Taylor and Filip Kiss dispatched the kick to level things up again.
Rhys Healey nearly grabbed a second when he cleverly juggled the ball with both feet in the area before hitting a shot on the turn but was thwarted by Alexander, but 15 minutes from time he did get on the scoresheet.
Harris found himself with time on the left and he waited before delivering a great cross into Healey's path, and he switched the direction of the ball across Alexander and into the far corner to complete the comeback.
With the Eagles trailing, Reise Allassani attempted something special to get Palace back into the game and nearly pulled it off when he embarked on a mazy dribble down the left flank and forced Moore to push the ball away, but the Welshman held on to secure their second victory in as many games this season.
Palace: Alexander, Taylor, Parr (Croll 46), Dymond, McCarthy (Gordon 55), Wynter, De Silva, Boateng, Sekajja, Grandin, Kaikai (Allassani 73). Subs not used: Fitzsimons, Sow.
Cardiff: Moore, Yorwerth, Owen, Kiss, Williams, Oshilaja, O'Sullivan (Wharton 80), Mutch, Healey, Mason, Harris. Subs not used: Matthews, Bowen, Roche, Southam.