This was the fourth time the two sides had met since September and with a third round tie away to Sockport County awaiting Martin Allen's team they will fancy their chances at having a decent run in the cup.
Both sides squandered early half chances with both Sam Sodje and Andy Liddell not making the most of their opportunities in front of goal for Brentford and Oldham respectively.
The game had barely got going when Sodje and Richard Butcher clashed heads in the centre circle with the latter unable to continue and was replaced by Gareth Owen with only 12 minutes on the clock.
Neither side could be faulted for their industry in the opening half, but there were few touches of real quality as both harried each other and were denied space and time at every turn.
Jay Tabb returned to the home side having recovered from injury and looked dangerous with his trademark runs cutting in from the wing, but he failed to find his range early on shooting narrowly wide from the edge of the box.
The home side almost opened the scoring just before the break when Owusu headed Paul Brooker's corner back across the box to the waiting Michael Turner, but his snap-shot was smartly saved by Chris Day from point-blank range.
First-half substitute Owen saw red midway through the second half when he got his second yellow card just minutes after his first.
Owusu finally broke the deadlock when he headed home from barely six yards out.
The impressive Tabb hit an excellent free-kick into a crowded box and Owusu out-jumped Marc Tierney, who had only just come on to the pitch, and headed past the helpless Day.