Ole Gunnar Solskjaer believes David de Gea has done away with distractions and regained focus after signing a long-term contract extension with Manchester United.
Star goalkeeper De Gea ended speculation over his future when he put pen to paper on a fresh four-year deal on Monday.
Long-running negotiations dragged into the new season and kept potential suitors interested but Solskjaer grew increasingly confident of tying down the Spain international.
The United manager now expects to see the best of De Gea following a significant dip in his form last term.
"Most of the time we get to keep the ones we want to keep," said Solskjaer.
"The more I got to listen and speak to David, I was pretty confident we were going to make it.
"David is delighted. I think you could see by his performance [in the Premier League win] against Leicester that he had made up his mind. You could see the focus in his eyes again.
"You do feel very secure with a focused David behind you.
"He's really worked hard this season. He's still young. Edwin [van der Sar] signed for us when he was 35, so I'm sure David will be part of a successful United team."
De Gea will be rested when the Red Devils commence their Europa League campaign at home to Astana on Thursday.
Sergio Romero is to replace the 28-year-old in goal with Fred, Axel Tuanzebe and Mason Greenwood to join him in the starting XI.
It will be a second senior competitive start for teenager Greenwood, a talent held in high esteem by Solskjaer.
"Mason is one of the best finishers I've seen and I played with quite a few decent ones," said the former striker.
"He's still very young but he's maturing and he's developed so much since I came in. I remember the kid who just wanted to play with his mates in the Under-18s. Now he's knocking on my door wanting to play these games.
"I don't want to put too much pressure on him. It's just about enjoyment, go out and express yourself at Old Trafford."