Pete Cowen revealed he laid down the gauntlet to fuel Brooks Koepka at Shinnecock Hills and can see the American winning more majors after clinching back-to-back U.S. Open titles.
Koepka held his nerve in Long Island on Sunday to become the first man since Curtis Strange in 1989 to successfully defend the U.S. Open trophy.
Cowen, Koepka's short-game coach, warned the world number four he would not realise his potential unless the 28-year-old improved his attitude before he won his first major at Erin Hills last year.
The Englishman, who also coaches the likes of Henrik Stenson and Matt Fitzpatrick, issued another challenge to ensure Koepka was fully motivated ahead of his latest triumph.
Cowen told Omnisport: "I'd been to Memphis the week before last year's U.S. Open and watched him play all four rounds and his attitude and body language was very poor, so I pulled him to one side on the Tuesday at the U.S. Open and said, 'Look, you're not going to win anything with that sort of attitude.'
"I challenged him again this year by saying, 'You want to make sure you keep hold of that trophy, it's a big challenge to keep it so make sure you do.'"
Koepka has established himself as one of the top players in the world and Cowen said he can go from strength to strength.
"He is a very cool character, he doesn't get stressed, he doesn't show any temper, snap clubs... You won't know if he's made a birdie or a bogey on the hole before. He's able to dismiss whatever has happened before almost instantly," he added.
"I've worked with him for the last five years and he's been like that all that time.
"You would say he can win more majors, he's young enough, he's number four in the world now and when you are at that sort of standard you are always capable of winning more. He is very talented and believed in himself [at Shinnecock Hills]."
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