Frozen out by former manager Ruben Amorim, Mainoo played a full 90 for United in the 2-0 win. Maguire, meanwhile, was rushed into the starting XI ahead of injury recovery schedule by Carrick.
The Geordie said: “Yeah, I thought Kobbie was great in there alongside Case (miro), I thought between the two of them.
"I thought it gave us a strong foundation really with Licha (Martinez) and Harry. I felt it was a game for experience and knowing what it feels like. It was a big ask for H (Maguire) and credit to him. I think we can take for granted sometimes what players do but for him to play today and come through it.
"I’m not going to lie, it was a bit of a calculated gamble as well of how long he could play and if he could get through it because he’s literally trained for two or three days for probably eight or nine weeks, so it just shows you what it means really to him. I thought he was fantastic.
"Between him and Licha, they were so solid at the back and gave us the foundation to build on.”