Billy Kee struck for Albion in the 27th minute with a fine turn and shot before Wycombe were reduced to 10 men after the break when Dunne picked up a second yellow card on 48 minutes.
Kee duly punished the Chairboys with his second, scoring from the spot four minutes later to seemingly kill the game off.
Matt McClure pulled one back for Wycombe in stoppage time but they have now not won for three games and were not helped by Dunne's sending off - his second of the season already.
But Ainsworth refused to condemn the 20-year-old, who is back at his former club on loan from Blackpool, despite insisting he must learn his lesson.
"We started the second half well, made a bit of pressure but then Charles was very rash and very silly," he said.
"It's a young pro's tackle - the last thing I said to him was to be careful. But I've been in that situation, I've been sent off before and as long as he learns from it that's fine.
"It was a rash challenge to do on a yellow card and he'll be feeling bad but it won't all be down to him.
"It didn't help with 10 men and then the penalty and a few decisions I didn't agree with, but I'm not one to talk about referees - I've got plenty more to worry about.
"I think the introduction of the young boys, Josh Scowen, Max Kretzschmar and Junior Morias affected the game. They came on, did well and that got us back into the game, the positives were there but we were way behind and it was a big uphill struggle."