Goals from Sean Rigg, Alfie Potter and Tom Craddock did the damage as Oxford, who had James Constable sent off midway through the second half, extended their unbeaten run to nine in all competitions. And Ardley, who took the reins from Terry Brown in October, did not hold back in his criticism.
"I've defended the players in the past and I'm not going to defend them after that," said Ardley. "I work hard along side my backroom coaching staff for every game. We think about what we have to do in training, but ultimately when you get out on the pitch it takes us until we're 2-0 for anyone to show any courage.
"There are too many weak mentalities. We're bottom going into the new year and I'm willing to have a go at this and make sure we don't go down. I need players who can show a bit of courage and show some balls.
"You have players that know how to win games and you have players that don't. For 25 to 30 minutes, there wasn't one player who took responsibility for their performance. Not one player did their bit that they were asked to do before the game."
Despite the three points, Oxford boss Chris Wilder was not all smiles at the final whistle with Constable's red card for an apparent elbow on Wimbledon's Will Antwi his main source of frustration.
"The ref got it wrong. The lads conned the referee and he's fallen for it hook, line and sinker," he said.
"There was a bit of a coming together and bit of banter between which, when I played, happened all the time. You were always winding players up and it's part of the game. All they were doing was having a nip at each other. The referee was sucked in.
"It is disappointing because it was a really good performance away from home. There was a lot of good individual performances and a brilliant collective performance too. It's another win and we're a bit closer to where we want to be.
"But I've lost a player who's absolutely flying for four big games now. I can't afford to lose anyone. We're gutted. A report and an appeal will go in 100 per cent. It's just ridiculous because you want to see the game played in the right way."