LOS ANGELES -- When Wyndham Clark was a child, his mother, Lise, liked to put notes of encouragement in his book bag. The notes might have been a source of embarrassment for Clark back then, but he certainly wishes his mother was around to see what he accomplished on Sunday.

Clark, who was ranked 293rd in the Official World Golf Ranking a year ago and had never finished better than a tie for 75th in a major championship, held off Rory McIlroy, world No. 1 golfer Scottie Scheffler and Rickie Fowler in the final round to win the 123rd U.S. Open at Los Angeles Country Club.

Clark, from Denver, carded an even-par 70 on Sunday. His 10-under total of 270 was one stroke better than McIlroy, who failed to end a nearly nine-year drought without a major championship.

Clark opened up a three-shot lead over McIlroy with four holes to play. Then Clark made back-to-back bogeys to trim it to one. McIlroy could manage no better than par in his final five holes, leaving Clark to win it on his own.

On the par-4 18th hole, Clark hit his tee shot down the right side of the fairway. His second shot was short of the green, leaving him 59 feet, 9 inches to the hole. With a gallery of hundreds of fans gathering on the fairway behind him, he calmly two-putted for the victory. He buried his head in his hands and hugged his caddie, John Ellis.

With early mistakes knocking Fowler and Scheffler out of the hunt, it was a two-man battle down the stretch between Clark and McIlroy, a four-time major winner. Clark, 29, had made the cut in two majors before this week. But after picking up his first PGA Tour victory at the Wells Fargo Championship five weeks ago, Clark's confidence swelled. He came into the week vowing to be "cocky."

Clark was that and more over the final 18 holes. He became only the fourth player in the past 100 years to win the U.S. Open in the first tournament in which they made the cut, according to the Elias Sports Bureau. Lucas Glover was the last player to do it in 2009.

Clark started the final round as the co-leader at 10 under with Fowler, a California native, who was trying to capture his first major championship. Clark picked up a birdie on the first hole and a bogey on the second. After adding two more birdies on Nos. 4 and 6, Clark avoided near-disasters on the final two holes of the front nine.

The par-5 eighth had been the easiest hole on the North Course all week, but it wasn't for Clark on Sunday. His second shot was nearly perfect but came up about a yard short and settled deep into native grass in a barranca, a deep gorge in front of the green. He had an awful lie and stance and swung under the ball on his third shot. Then he popped his ball out and over the green. He had a great chip to about three feet to save a bogey. It could have been worse. He dropped to 11 under after eight holes, one ahead of McIlroy and three in front of Fowler.

Then, on the par-3 ninth, Clark's tee shot was short, and his ball settled in the native grass again. He had a near-perfect chip shot above the hole, and his ball rolled down the green to about six feet. He knocked in the putt and made the turn at 1-under 34.

Fowler and Scheffler both carded back-to-back bogeys in the first three holes of the second nine, dropping them to 6 under and 5 under, respectively. After that, it was all but down to Clark and McIlroy.

Clark and McIlroy both posted pars on each of the first four holes on the back. Then there was a two-stroke swing on the par-5 14th. McIlroy's third shot became embedded in a greenside bunker. He received a free drop but couldn't get up and down. He missed a nine-footer for par and made a bogey, dropping him to 9 under. Clark narrowly missed an eagle putt on the 14th after reaching the green in two shots. He settled for a birdie, opening up a three-shot lead over McIlroy with four holes to play.

It might have been Father's Day on Sunday, but Clark's late mother was undoubtedly on his mind. Lise Thevenet Clark grew up in Albuquerque and attended New Mexico State. In 1981, she was crowned Miss New Mexico and competed in the Miss USA pageant.

She moved to Los Angeles, where she sold cosmetics for Mary Kay. In April 1989, she married Randall Clark, a former professional tennis player. In 1990, their daughter, Kaitlin, was born. After the family moved to Denver, Wyndham was born in 1993. His younger brother, Brendan, came along in June 1997.

Six months after her youngest child was born, Lise Clark was diagnosed with breast cancer. She endured rounds of chemotherapy and radiation for two years until she was diagnosed as cancer-free in 2001.

Lise Clark introduced her older son to golf. Wyndham grew up playing at Cherry Hills Country Club. His mother passed the baton to her husband, who started playing the game when Wyndham was three years old.

"My mom first took me to play golf, but my dad was the one that really got me into golf," Clark said. "Every time I'd go golf at a young age, it was with my dad. There's so many memories of us leaving at 6 a.m., our family on like a family vacation and we'd come back and play golf before noon, and that was the only way my mom would let us do that."

Clark said his father instilled in him "hard work and discipline."

"I feel like I get a lot of my fieriness from him," Clark said. "So he's given a lot."