Christophe Berra's close-range finish in the 81st minute and David McGoldrick's free-kick six minutes from time, his 16th goal of the season, cancelled out strikes from Barnsley pair Chris O'Grady and Tomasz Cywka to earn a 2-2 result.
The draw extended the Tractor Boys' unbeaten run to four games and moved them to within three points of the Sky Bet Championship top six, while leaving relegation-threatened Barnsley four points adrift of safety.
McCarthy said: "It looked like being the most one-sided two-nil defeat, at nine minutes to go, there's ever been.
"We played well in the second half, we had enough chances to win it. (We were) profligate and let them off the hook.
"The players kept going, we rallied them on and we got what we deserved. In fact, I don't think we got what we deserved, I think we should have won.
"It's a blooming good point from two-nil down with nine minutes to play. I thought if we got one back we might win it."
Born in the town, former Barnsley player McCarthy said: "I love coming back and I usually get my a**e slapped when I come back; I nearly did again.
"You heard them singing 'Mick McCarthy is a Red'. I am and I always will be but they don't give me anything when I come back and I don't give them anything lightly, and that's the way it should be.
"They wouldn't have liked me as much as they did as a player if I gave things away."
- Sports & Recreation
- David McGoldrick
- Christophe Berra
- Mick McCarthy