Rooney was at the game as a pundit and said: "I think you find with young players, when they pick the ball up, they're always very direct but that works really well for him so often.
"It's sloppy from (Ben) Godfrey to give the penalty away, but for me today, it was Garnacho who was the one that made everything happen today.
"He was the best player on the pitch. His work rate off the ball is fantastic, he's never afraid to put the work in.
"He's going to make mistakes, every player does, especially at his age, but he's still learning and what he has got is a drive and hunger which is something that any fan wants to see in any player so I've been really impressed with him this season and he'll be a talent for the future.
"I think his output can get better, he's got the capability to do that so hopefully over the next few years, we'll see those go up, but he's probably been Manchester United's best player this season."