THE FINAL round of the US Open usually falls on Father’s Day, but Wyndham Clark spent plenty of Sunday thinking about his mother.

As he made his way around the Los Angeles Country Club’s North Course throughout the week, Mr. Clark only wanted his late mother Lise Clark, who died of breast cancer in 2013, to be there to soak it all in with him.

“She’d be crying tears of joy,” Mr. Clark said Sunday. “She called me Winner when I was little, so she would just say, ‘I love you, Winner.’”

Now he’s a major championship winner.

Mr. Clark posted an even-par 70 to outlast Rory McIlroy, announce himself on the major stage and claim the 123rd US Open for the first major title of his career on Sunday in Los Angeles.

With a final total of 10-under 270, Mr. Clark won by a single shot over the Northern Irishman desperate to end his nine-year major drought. At the 72nd hole, Mr. Clark lag-putted from 60 feet to set up a tap-in par, unleashing a fount of emotion amid his celebration.

Mr. McIlroy also shot a 70 and didn’t make a birdie after the first hole, never putting enough pressure on the less experienced Mr. Clark.

World No. 1 Scottie Scheffler (70 on Sunday) placed third at 7 under, Australia’s Cameron Smith (67) was fourth at 6 under and Rickie Fowler shot a 75 to drop into a tie for fifth at 5 under with Tommy Fleetwood of England (63) and Min Woo Lee of Australia (67).

Mr. Clark and Mr. Fowler held the 54-hole lead at 10 under after Mr. Fowler missed a short par putt on the 18th Saturday night. They played in the final pairing for the second straight day Sunday, and it was understandable if the majority of fans were pulling for Mr. Fowler, a longtime PGA Tour fan favorite.

After a birdie-bogey start, Clark stuck his tee shot at the par-3 fourth to 5 feet and his approach at the par-4 sixth to 4 1/2 feet, converting both birdies to reach 12 under. At the par-5 eighth, he was unable to punch out of some grass nearly as tall as him on the first try, and he skied his next shot before winding up with a bogey 6.

Mr. Clark missed the green at the par-3 ninth but gave an emphatic fist pump when his 7-foot par putt dropped, the first of five enormous par saves in a row before the pivotal par-5 14th.

Mr. McIlroy’s approach shot at No. 14 fell dropped short in a greenside bunker, and even though he was given relief because his ball was embedded, he failed to save par from 11 feet. Mr. Clark followed behind him with a birdie, effectively a two-shot swing that gave Mr. Clark a three-shot cushion with four holes to play. — Reuters