Mackay had given Bellamy just 18 minutes of action since the last international window, and admitted he had done so partly with the derby - and the impact he knew the striker could make - in mind.
He said: "When it came to the derby, I felt there was experience there.
"He has been mature over the last two years since I have been here, even more so this year as he has called time on Wales and he knows the sun is going down on his career.
"But he has been immense this season on and off the field, whether he has not been picked, whether he has been starting, used as a substitute or being asked to train hard.
"Having him on the field in that derby was something I really wanted, we spoke about it during the week and I think his experience showed.
"He got a second wind with 10 minutes to go which I hadn't seen before and I don't think he had seen either.
"It's one of those where he showed experience through the day."
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