An unsung American hero has emerged at the U.S. Open.

Michael Mmoh pulled off a 6-2, 6-4, 6-2 upset first-round victory over Karen Khachanov, the World No. 11, 6-2, 6-4, 6-2 in front of a rowdy crowd on Court 12 on Tuesday.

The Russian, who seemed unprepared, had not played since the French Open in June due to a stress fracture and a partial fracture in his hip and groin. At Roland Garros, he lost to No. 2 Novak Djokovic in a four-set quarterfinal match.

“[Khachanov] got to the semifinals here last year. He’s a bigger name than me. So, to have the crowd behind my side, it was a pretty special feeling,” Mmoh said following the match. “I played [Gilles] Simon here last year and the crowd was on his side. So, to play a guy that’s even more accomplished and the crowd’s on my side is pretty cool.”

Mmoh added another crucial win to his belt during what already has been his career best yet.

The 25-year-old, who is ranked 89th, made it to the third round of the Australian Open, including a win over Alexander Zverev. At Wimbledon, he took out No. 15 Felix Auger-Aliassime in the first round.

“It’s tough to pick between all those wins. Like it’s your children, you know,” Mmoh said with a laugh. “All of them are special, but like you said, to do it in dominating fashion, it does hit a little different. It gives you a little confidence, rather than if you battle against somebody and you squeak it out.”

In the final set Tuesday, the first two games went to deuce with each player taking one.

Khachanov attempted to play near the net to get in Mmoh’s face, but the American kept dealing out powerful deep shots, meeting Khachanov at his feet or lagging behind.

Mmoh broke Khachanov’s serve in both the third game and seventh game, beating the Russian in the latter with six break points.

In the final game, Khachanov’s netted ball tied the bow on Mmoh’s sweet victory, a reminder of Frances Tiafoe’s Cinderella story last year in reaching the U.S. Open semifinals, as well as Chris Eubank’s quarterfinals showing at Wimbledon.

“Yeah, I feel like we’ve had a lot of parallels the last couple of years,” Mmoh said of Eubanks. “He’s a lot higher than me now with the quarterfinal run, but I think we’re both moving in very similar directions. And, it just goes to show you that you never know when it’s going to be your time and you just got to stay ready for when it does happen.”

Mmoh explained he changed his game by doing a lot of things he wouldn’t normally do, such as reading books for advice, and taking pointers from those around him such as Coco Gauff’s dad.

“This was last year at Wimbledon, so I was playing [qualifiers] and he was saying that African Americans for whatever reason, especially on the male side, they don’t really peak until they’re like 25, 26,” Mmoh said. “And he’s giving me all types of examples: [James] Harden, he didn’t really peak until he was 26, 27. LeBron [James] didn’t win a chip until he was 26, 27. So, he was like, just wait until you’re that age

“It kind of just hit me in that moment like, all right, so maybe I just gotta wait until I’m 26, 27. Right now, 25, so maybe my true peak is gonna be in a couple of years.”

If Tuesday was telling for the rest of the tournament and future of tennis, there will be more to see of Mmoh.

For now, he will play soon-to-retire John Isner, a fellow American, with whom Mmoh has grown to be friend. Before Isner’s win, he said he hoped to face him on Wednesday in the second round.