It was 0-0 at half time after a poor display from both sides but all that changed when Aaron Brown and Latics old boy Paul Warne hit the target in the second half.
Yeovil, with only one away win and three goals all season, turned the contest on its head with their quick-fire double.
A free-kick into the box from Gary Roberts was met by Brown who connected with a perfect header in the 62nd minute.
Two minutes later Warne, who was a fans' favourite during a two-year spell at Boundary Park, put the game out of reach.
He chased a long ball out of defence from Craig Alcock to turn and shoot past Mark Crossley from 10 yards out. Earlier Oldham had chances but couldn't get past giant Canadian keeper Asmir Begovic.