LOS ANGELES — As he walked down the eighth fairway on Sunday afternoon, the leader of the U.S. Open might as well have been a ghost. Most of the gallery at Los Angeles Country Club was too busy screaming encouragement to fading Rickie Fowler to pay any attention to Wyndham Clark.

You got this, Rick!

Let’s go, Rickie!

You’re more handsome!

Then one middle-aged heckler finally addressed Clark and didn’t hold back.

“Sorry, Wyndham, we don’t really care about you,” he shouted at Clark. “We don’t know your story yet.”

They know Clark’s story now. They know about how his mom’s death almost drove him to quit the sport, how he didn’t notch a win on the PGA Tour until last month and how he is now only beginning to tap into his potential. They know that he was a 60-to-1 long shot to win the U.S. Open coming into the week. And they know that on Sunday evening he did just that, holding off a four-time major winner and the face of the PGA Tour no less.

Clark shot even par 70 in the final round of the U.S. Open on Sunday to finish 10-under for the tournament and edge Rory McIlroy by a single stroke. Though he bogeyed Nos. 15 and 16 down the stretch to turn a three-shot lead into a white-knuckle ride, Clark managed to slow down and refocus just in time.

McIlroy was steady, scoring par at No. 18 to stay within striking distance. Clark was even steadier, tapping in at 18 for the most important par of his life and then screaming “yes” and double fist pumping in celebration of a career-altering victory.

“I feel like I belong on this stage,” Clark said. “Even two, three years ago when people didn't know who I was, I felt like I could still play and compete against the best players in the world. I felt like I've shown that this year.”

Perhaps adversity on the golf course doesn’t faze Clark because he has been through much worse away from it. Lise Thevenet Clark died of breast cancer at age 55 in August 2013, sending her eldest son into a tailspin.

“I didn't show any emotion off the course, but when I was on the golf course I couldn't have been angrier,” Wyndham said. “I was breaking clubs when I didn't even hit that bad of a shot. I was walking off golf courses.”

Lise was Wyndham’s confidante and an endless source of encouragement and positivity. Before she died, the mantra she instilled in Wyndham was to “Play big.”

Without his mom, Wyndham struggled with confidence. He transferred from Oklahoma State to Oregon after one “really low spot.” Then he hit another rough patch early in his professional career when he again struggled to tap into his immense potential.

People would tell Clark, “Oh, you have such a great swing,” yet he had no idea where the ball was going. Until this past week, the 29-year-old Denver native had never made the cut at a U.S. Open, nor finished better at a major than a tie for 75th.

“Those first few years on tour, I felt like I underperformed,” Clark said. “I've had many times where I've gone home and was yelling in my car and punching things and just so mad. I'm like, ‘Why can't I do what my peers are doing?’ ”

For Clark, the path to hoisting the U.S. Open’s sterling silver trophy began in November when he began working with a mental coach. She instilled a sense of calm and belief in Clark that he had been missing since his mom’s death.

It also helped Clark when he ditched the swing coaches he had worked with and took charge of his own swing. Drastically improved iron play has fueled Clark’s rise this season, helping him pile up top-25 finishes and capture his first PGA Tour victory in May.

Clark was the outlier on a Sunday leaderboard loaded with fan favorites and previous major champions, but he never once questioned whether he belonged. Every time he heard someone chant “Rickie” or “Rory,” he harkened back to advice he received from his mental coach.

“Think of your goals and get cocky and go show them who you are,” she told Clark.

“I did that,” he said. “It was like 100-plus times today I reminded myself of those goals.”

A difficult up-and-down on the eighth hole was one key point in Clark’s round as it allowed him to maintain a one-shot lead at the turn. Then came a big two-shot swing at No. 14, Clark hitting a spectacular approach shot and tapping in for birdie minutes after McIlroy had his only bogey of the day at the hole.

Clark seemed to be in position to win comfortably, but this is the U.S. Open after all. He, in his words, “hit a terrible wedge shot” at the short par-3 15th and became the only player in the field to bogey the hole. Then he drove into a bunker at No. 16 and narrowly missed a putt to save par.

“Although I made a couple bogeys and it seemed like maybe the rails were coming off, inside I was pretty calm,” he said.

At the 18th tee box, one par away from a career-altering victory, Clark surveyed the fairway in front of him and formulated his plan of attack.

“Same shot as the last three days,” caddie John Ellis told him. “Same wind, same club.”

Except there was nothing familiar about this moment for Clark. This was unlike anything that he had ever experienced before. He found the fairway with his drive, then the green with his approach. Clark teared up as he walked the 18th fairway, but he steadied himself once more. Two putts later it was over. He’ll forever be a major champion.