For many connected to United it was Mainoo's best performance for the club.
Kobbie didn’t train an awful lot really,” Carrick said afterwards.
“He only did a little bit on Thursday and a little bit more yesterday. I wasn’t an awful lot, so credit to him for stepping into that one.”
Carrick also said: “I thought that was the best Kobbie’s played, certainly since I’ve been back here.
“To step up and put so many phases or sides to his game tonight… I thought he looked so composed and so calm, he had a real presence about him, defended well.
“It’s not easy when you’ve got good players around you and it was a good battle between him and Cole Palmer.
“So he had to be right at it tonight but as you saw he had so much quality and composure in a tough environment really, to show us what he can do.”