ERIN, Wis. — The back-to-back birdies to start the round were big. So, too, the shot out of the bunker on 14. And that birdie putt on 15 that kept everyone at bay? The definition of clutch.

Truth is, though, Brooks Koepka won his first major back in October.

If not for the crushing pressure of the Ryder Cup, Koepka wouldn’t be the new U.S. Open champion. Keeping your composure — and cushion of a lead — down the stretch will barely cause you to break a sweat after you’ve survived three days’ worth of jangling nerves and stomach in a constant state of free fall.

“I feel probably a lot more comfortable than I have probably in the past,” Koepka said after the third round, which ended with him one stroke behind leader Brian Harman. “The Ryder Cup helps. It’s kind of simple. I think that’s probably the most amount of pressure I’ve ever played in. When you look at that, just kind of build off the experiences out there.”

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Indeed, when he made his par putt on 18 to secure his four-stroke victory Sunday afternoon at Erin Hills, he gave only a small fist pump.

Not until several minutes later, when he was in a golf cart heading back to scoring, that he buried his head in his hands, overcome with the enormity of both what he’d done and what he’d won.

“It’s unbelievable,” he said. “I don’t even know what to say right now but it’s pretty cool.”

Koepka is the seventh consecutive first-timer to win a major, extending a run that started with Jason Day’s win at the 2015 PGA Championship. It was all but a given that the newbie streak would continue; Sergio Garcia and Louis Oosthuizen were the only major winners in the top 25 going into Sunday’s final round and, at eight strokes back, neither figured to be much of a factor.

To win a major takes talent, of course. But even more important is grit, and Koepka had more of that than anyone else.

His 5-under 67 was the second-lowest round of the day. He made only one bogey. He missed only one green.

He played as if he had been there before — no easy feat when you haven’t.

“I felt so confident out there,” he said.

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Koepka had a PGA Tour win, along with a handful in Europe and Asia. But a major is a completely different beast. You are leaving a mark in history, your name forever joined with Ben Hogan, Arnold Palmer, Jack Nicklaus, Tiger Woods.

The magnitude of such a moment can be overwhelming. Look at Justin Thomas, who got flustered when a gust of wind on the No. 4 green blew his ball 4 feet back from the hole. He made bogeys on consecutive holes and was never a factor again.

Brian Harman had not bogeyed a hole on the back nine all week until he drove into a tangle of fescue on the 12th. He would miss his par putts on both 12 and 13, along with one on 18 that would have given him sole possession of second place.

Hideki Matsuyama, Tommy Fleetwood, Rickie Fowler, Charley Hoffman — each had his chance and each one faltered.

For Koepka, the difference was his experience at last year’s Ryder Cup.

It’s never easy to be a rookie at the Ryder Cup, a fevered international competition. But even less so last year, as the Americans tried to win the Cup back for the first time since 2008.

Koepka talked of being so nervous he worried about keeping his ball on the tee. Yet he exuded a calm swagger, and wound up as one of the most productive Americans. He collected three points from four matches, including a 5&4 rout of Masters champion Danny Willett.

The confidence he drew from that, along with strong showings at the British Open and PGA Championship, separated him from the pack as much as his booming drives and precision on the greens.

Koepka’s performance at the Ryder Cup helped the Americans win the coveted trophy. Six months later, it helped him win another.

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Follow USA TODAY Sports columnist Nancy Armour on Twitter @nrarmour.

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