Kieran Richardson's goal early in the second half looked to have given the perfect welcome gift to former Aston Villa manager O'Neill, who was watching from the stands at Molineux ahead of his first day in charge on Monday.
But Sunderland winger Sebastian Larsson saw his penalty saved by Wolves keeper Wayne Hennessey before two goals in quick succession from Steven Fletcher gave Wolves a vital win.
It moved them four points clear of the bottom three in the Premier League with only their second victory in 12 games and left O'Neill to take charge of a team sittng only one point and one place above the relegation zone.
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 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.
"I don't do advice; I'd take some off him if he wants to give it!"
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."
Despite another dispiriting defeat, Blacks Cats caretaker boss Eric Black -- who is likely to follow sacked boss Steve Bruce out of the club -- believes O'Neill will revive Sunderland's fortunes.
"Martin will have seen the strengths that we have. I think he knows there are some good things to take forward," Black said.
"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."
Black felt the penalty save by Hennessey was the pivotal moment of the game.
"If the penalty had gone in, you'd like to think we'd have gone on and won the game," he said.
"I thought that was the pivotal moment in the whole of the game. I don't want to blame the person who took it because I think Seb Larsson has been outstanding this season.
"But the confidence and energy drained a little bit when it didn't go in and the rest of the game became hard for us."
Source: AFP
Source: AFP