Doyle finger-tipped a powerful drive from Wolves winger Matt Jarvis on to the post and then reacted quickly to keep out Steven Fletcher's close range follow-up header.
It means the two sides must replay at Molineux on January 17.
Blues boss Hughton said: "It was a brilliant save at the end. It kept us in the tie.
"That is the thing with keepers. They cannot be too troubled for most of the game which was the case today.
"But we certainly needed Colin at that moment and it earned us a replay."
Wolves boss McCarthy said: "I think the game was going to be decided on something daft or a fabulous bit of football.
"As it turned out it was decided on something brilliant.
"It was almost a brilliant goal from Jarvo's initial strike and then two brilliant saves from Doyle kept it all square."
Hughton admitted Birmingham would have preferred to avoid a replay as they are still playing catch-up with their Championship fixtures after their Europa League campaign.
But he is happy to still be in the competition and is backing his squad to cope with the extra demands.
He said: "We are disappointed today. I still think with Wolves, as the Premier League team coming here, there was more pressure on them to win here than ourselves.
"But it is another fixture. We could have done without the extra fixture with the amount of games we've got coming up.
"But I think the feeling is we've delighted we are still in the competition and we will have to deal with what lies ahead.
"We didn't play to our maximum today. I don't think Wolves did either. A draw was a fair result.
"If they had got the goal at the end, it certainly would have been unjust. I don't think they deserved to win so probably it is a fair result and we have to go again on Tuesday week."
McCarthy echoed Hughton's sentiments and said: "Undoubtedly, I'd rather draw and still be in this competition."
Hughton admits Blues are hoping to extend the loan deal of West Brom striker Chris Wood with the current arrangement expiring on January 5.
He said: "At this moment, Chris is a West Brom player. He's gone back to West Brom. His loan has finished and was in their squad today.
"But we've been in regular communication with West Brom and he is one we'd like to bring back."
McCarthy is relieved former Blues defender and Wolves captain Roger Johnson escaped without any serious damage to his ankle after he was substituted during the first half-time.
He said: "Roger rocked his ankle on Friday and, as he landed, he did it again. He wanted me to give him five minutes but, having done it twice, there was no chance.
"I would not take that risk. Damage your ligaments you could be out for a month or six weeks - but he's fine."