Vicente Guaita's howler gifted Harry Kane a 15th goal of the season midway through the first half to silence the 2,000 fans who were allowed to return to Selhurst Park on Sunday.
Schlupp spared his goalkeeper's blushes nine minutes from time, though, prodding in from close range when Hugo Lloris failed to deal with Eberechi Eze's inviting free-kick.
