Kieran Richardson looked to have given the perfect tonic to the watching O'Neill, who will officially take charge on Monday, with a stunning opener but then Sebastian Larsson saw a contentious penalty saved by Wolves keeper Wayne Hennessey, before two goals in quick succession from Steven Fletcher saw Wolves gain a vital win.
When McCarthy was asked if he had any advice for O'Neill, the former Sunderland boss said: "No, I'm just glad I've made his job harder for on Monday morning. I'm thrilled that's he's got a harder job than it looked like for however many minutes here. Martin is a pal of mine but I didn't want to do him any favours."
Fletcher has now scored 10 times in his last 15 Premier League appearances for Wolves, and McCarthy said: "When he's been fit, he's been terrific. That's why I signed him.
"When he's had injuries, they've been impact injuries, something he can't help. Keep him fit and he's a very good player. When he's been fit, he's been prolific for us."
Replays appeared to show there was minimal - if any - contact from Jody Craddock on Larsson when he went to ground for the penalty.
McCarthy said: "Jody insisted he didn't touch him and apparently he didn't. But, if it was a dive, then they got what they deserved and the penalty save certainly was a catalyst.
"The game turned on its head with that moment."
Blacks Cats caretaker boss Eric Black believes O'Neill will revive Sunderland's fortunes.
He said: "Martin will have seen the strengths that we have. I think he knows there are some good things to take forward. But I think he'll also know that there are some problems. I'm sure he'll start on Tuesday trying to rectify those problems."
Source: PA
Source: PA