The Gunners’ top-four hopes were dealt a serious blow after goals from Christian Benteke, Wilfried Zaha and James McArthur sealed a memorable win for the Eagles.
Mesut Ozil and Pierre-Emerick Aubameyang led the hosts’ fightback, but the match hinged on a moment of madness from Mustafi, who inexcusably allowed Zaha to latch onto a seemingly-harmless ball and put Palace 2-1 up.
It was the latest in a string of Mustafi errors which have cost the Gunners this season, but Emery refused to criticise the German.
“I’m going to protect every player because they worked and tried to do their best possible,” he told talkSPORT.
“I think we can speak about them all generally and not focus on individual issues.”
The Arsenal boss admitted his team missed a big opportunity to climb into third and seize control of the top four on an Easter weekend which also saw Tottenham and Manchester United slip up.