The Eagles were trailing to Daniel Bogdanovic's ninth minute goal when the Eagles youngster's brilliant overhead kick beat Barnsley keeper Lee Steele early in the second half.
There was a lively opening to the match at Selhurst Park and Bogdanovic had a chance in the opening seconds but his shot was pushed away from danger by Julian Speroni.
Palace had a golden chance to go ahead less than a minute later when Ryan Shotton produced a clumsy challenge on Moses inside the box but Darren Ambrose's spot-kick clipped the top of Steele's crossbar.
The Barnsley number one made an excellent reaction save on 13 minutes, clawing away Clint Hill's header from an Ambrose corner.
But it was Hill's error which gifted the visitors a 19th minute opener. Anderson Silva poked the ball away from the Palace defender and Bogdanovic raced through to drive the ball past Speroni.
Moses was denied in the 24th minute when he appeared to handle inside the box as he latched onto Speroni's long kick before cracking off a right-foot shot which Steele managed to parry.
Palace's attacking play began to look laboured as the half wore on and they were desperately in need of inspiration.
They got exactly that on 52 minutes with a special finish from Moses.
Alan Lee flicked on Jose Fonte's free-kick and the striker chested the ball before sending his acrobatic strike into the net from the edge of the box.
Bobby Hassell went close to scoring an own goal when a quick Moses throw released Freddie Sears down the right, his low cross was sliced for a corner by the Barnsley right-back.
Palace continued to press for a winner and Hill and Lee both had chances but their headers were collected comfortably by Steele.
Barnsley struggled to create chances in the second half and winger Emil Hallfredsson had their best opportunity with six minutes remaining.
He fired in a dipping shot from 20 yards out which a back-pedalling Speroni palmed over his bar.