Kewell took over the League Two side a month ago, and got off to the perfect start with Ben Garrity, Bobby Grant and Conor McAleny scoring to seal the victory for the Aussie.
Oldham kick-off their League Two campaign next weekend against Leyton Orient.
The former Socceroos winger said he was 'over the moon' after the match.
"I felt the team stuck to their jobs. We knew it was going to be a challenge, but we handled it well," Kewell said.
"We're not getting carried away, we re-set ourselves now and we look forward to playing next weekend.
"The players have been working hard in pre-season, the performance we saw today deserved the win."
"It's been fantastic (to work here), hopefully we can get this place rocking again."
