Potter netted a first-half header and Powell scored a superb solo goal before defender Antony Kay was sent off on his home debut for violent conduct after the final whistle.
Dons bossed the first half and Potter stole in unmarked to head home Dean Bowditch's corner to put them ahead after 34 minutes.
The home side had chances to double their lead in the first half, but Ryan Lowe poked the ball wide when one-on-one with Alex Cisak and Daniel Powell crashed an angled drive against the crossbar.
Oldham rarely threatened, but Dons goalkeeper David Martin had to be alert to claw wide a cross-shot from Youssouf M'changama.
Powell made it 2-0 in the 59th minute when he burst into the box and fired a fine left-footed finish into the top corner before Kay was shown red for lashing out at Oldham striker Robbie Simpson in the closing stages.