Victory over against Blackburn at Molineux will ensure top-flight football for another campaign barring a freak set of results during the final two games which would alter a goal difference currently significantly in Wolves' favour.
And, while Kevin Doyle has earned the plaudits for his performances as the lone striker, McCarthy is also quick to recognise the contribution of Hahnemann, who will be 38 in June.
The American was signed from Reading on a free transfer last summer and initially had to play second fiddle to Wales international Wayne Hennessey.
But McCarthy decided to make a change between the posts in late November and since then Hahnemann has been an ever present and played a significant part in Wolves' survival battle.
It prompted McCarthy to offer Hahnemann a new contract in early 2010, long before Wolves knew which division they would be playing in next season.
McCarthy said: "Marcus has had a huge impact. Wayne was fabulous last season but he'd had no Premier League experience and I was aware of that when I signed Marcus.
"When I knew he was on a free transfer last summer, that was one of my first phone calls. I rang him very early in the summer. I think he'd only just got back home (to America).
"I knew all about him but I was very surprised he was available, I have to admit, so I was thrilled to get him.
"Marcus, to his eternal credit, accepted the fact Wayne was number one and he had to dislodge him.
"But he came into the team at a time when I thought we needed more solidity and experience and he came in and played very well. That's why he's kept his slot."
Hahnemann was happy to sign an extension, irrespective of where Wolves would be playing next season.
McCarthy added: "Marcus had a contract whereby if we stay up, and he played a certain amount of games, he gets a new deal.
"But I approached him way before that and said that, irrespective of where we are, I want you to stay and he was delighted by it."
McCarthy also knows Hennessey can have no cause for complaint about his long absence from the side given Hahnemann's form.
He said: "I spoke to Wayne at the time when I changed it and then afterwards, but there was no animosity from him. He just wanted to know what he had to do
"We had a discussion and he's been fine. Listen, if someone is playing as well as Marcus, you don't come knocking on the manager's door.
"If we had shipped three or four goals in a few games and Marcus was at fault and I wasn't changing it, I'd expect him to come and knock on my door - but that has not been the case."
McCarthy will take nothing for granted regarding Wolves' future and knows Blackburn will want to spoil the party atmosphere that would inevitably engulf Molineux if top-flight football is guaranteed.
He said: "We would love to confirm our safety. It's funny sometimes that the more you want something and crave it, the harder it becomes.
"It would be great to get three points and ensure our safety but it might happen, it might not. We'll do our best that's for sure. I don't want anyone else to help us out. I'd like to confirm it ourselves.
"But we're up against a Blackburn team who are coming to us to try and win points and finish as high up the league as they can. They will make it really difficult for us.
"That's for their own kudos and for them to make it as good a season as they can have. They've got some very capable players and are a difficult team to beat.
"They will not want to come here and be part of our party and the fact that if we win, we will stay up and there'll be plenty to celebrate for the fans."