Super-sub Jeff Goulding scored a superb goal to give Cheltenham a 1-0 victory after Barnet had missed a penalty.
The striker had been on the field less than a minute before finding the net with his first touch, a curling 25-yard effort beyond the reach of goalkeeper Graham Stack 10 minutes from time.
Chances were at a premium in the first half as the players struggled with the driving rain. Barnet's Mark Byrne forced a save from Scott Brown midway through the half with Shaun Harrad firing wide at the other end.
But the game burst into life after break with Graham Stack forced into two excellent saves to keep the Robins at bay.
He dived full-length to palm away a Chris Zebroski effort six minutes into the half and then managed to turn a deflected Harrad strike around the foot of the post on 70 minutes.
There had been drama at the other end five minutes earlier when Cheltenham's Darren Carter was penalised for handball only for Brown to keep out Byrne's spot kick.