Having won four of their previous five U21 Professional Development League 2 games, Palace were brought back down to earth after being beaten at Nottingham Forest.
Goals either side of half-time for the hosts clinched all three points and saw the Eagles slip to fifth position in the table but still only two points away from a play-off place.
Forest registered the first real chance on goal when winger Oliver Burke was picked out in the header but ballooned his header over the bar from a good position.
But the in-form Eagles showed their goal threat when Hiram Boateng swung over a corner which Michael Chambers headed towards goal at the back post, and after Reds keeper Ross Durrant pushed the ball away Connor Dymond's overhead kick flew over the crossbar.
Just before the half hour mark though Forest grabbed the opener. After finding space on the right, Illias Polimos drilled a centre across the face of goal and striker Tyler Walker was on hand to nip in front of the Palace defence and lash the ball home from close range.
Straight from the kick-off Burke came close to adding a second when he again found space on the right and charged into the final third, but flashed his effort just wide of Lewis Price's far post.
Gary Issott's side had a good chance to level things up before the break when Kyle de Silva embarked on a fine run through the Forest defence to give himself a shooting opportunity from the edge of the box, but just as he pulled the trigger he slipped and saw his attempt drag wide of the upright.
Boateng then forced Durrant into a good save right on the stroke of half-time as Palace pushed to find an equaliser, but it was Price was was called into action first in the second half when he saved a 25-yarder from the lively Burke on 55 minutes.
But after a quiet quarter of an hour Palace fell two goals behind on 70 minutes in unfortunate circumstances. A speculative cross from Wilfried Gnahore on the left found Josh Reece who shanked his shot well wide of the target, however it cannoned off a Palace defender and fell kindly to Matthew Cash who had the simple task of finding the net from eight yards out to clinch the victory.
Palace: Price, Egbo, Chambers (Allassani 70), Magri, Croll, Boateng, Dymond, Gray, de Silva (Adarbioyo 65), Kaikai, Johnson. Subs not used: Gregory, George, Black.