During her first-round match here at the US Open Junior Championships, Katherine Hui saw a small hand-held fan sitting near the side of Court 13.

During one of the changeovers in the first set, she picked it up and began playing with it, and showed it to her father, Yan Hui, sitting at courtside.

They shared a laugh, and that one moment, Yan Hui told his daughter after, was the highlight of the entire tournament for him.

“Even if you win it all, that was the best moment,” Yan Hui told his daughter.

Well, sitting a few feet away while his daughter had the greatest tennis moment of her life Saturday night, Yan Hui might’ve reconsidered that thought.

Because his 18-year-old daughter is now a Grand Slam champion.

Showing poise and mental strength when it counted most, and then surviving a wobble at the end that saw six match points fly by unclaimed, the San Diego, California native captured the girls' singles crown at the Billie Jean King National Tennis Center.

In defeating Czechia’s Tereza Valentova 6-4 6-4, Hui completed a dominant run through the girls' draw and became the second American girls' champion in three years, following Robin Montgomery’s triumph in 2021.

The Stanford University freshman didn’t drop a set in six matches, and never let an opponent get more than four games in any set.

“It was my last junior tournament, so I really wanted to make the best of it,” a beaming Hui said after the match. “I knew she was going to come out and fight, and I knew that I was capable of it as long as I trusted myself.

“I'm really proud of the way I played.”

Hui, who becomes the first US Open girls' winner to attend college since 1982, looked to be in total command of the match once she recovered from a rough start. Valentova, the hard-hitting ninth seed, jumped on Hui from the start, but Hui’s deep, penetrating groundstrokes and solid serving brought her back to win the final four games of the set.

“It didn’t go how I thought it would,” Valentova said. “I wanted to try to enjoy the match, but playing her was a very different game. She played really good and I hope to get more matches against her in the future.”

The second set was all Hui, as she raced to a 5-1 lead. But with the finish line in sight, Hui finally showed some nerves.

Valentova held for 2-5, then broke serve and held again, as five match points came and went.

“I think I did get some nerves,” Hui said. “Obviously I have never been in the final of a junior slam.

“It was a little bit of that, and I think she did step up and I give her a lot of credit for it. I think she started playing really freely.”

But finally, Hui steadied. At 5-4, deuce, Hui induced a Valentova error, and on match point No. 7, a strong first serve down the middle forced a long forehand return from Hui, and the Californian could smile and relax before going to hug her Dad.

“I’m just happy,” Yan Hui said. “I didn’t have expectations she would do this. This is not easy. For her it’s such a great way to finish her junior career. I can’t believe she did this!”

Valentova said she hopes to compete in the ITF World Tennis Tour Junior Finals in October, an event for the top eight-ranked juniors in the world.

While Hui was in the early stages of her match with Valentova on Court 12, she did hear periodic noise eruptions from Arthur Ashe Stadium, as Coco Gauff was finishing off her historic women’s singles win.

“I heard some really loud roars come across, so I just assumed she won,” Hui said. “Yeah, it just got louder and louder. “She's obviously such a big inspiration to me. I never met her or anything, but, I mean, just being that young and accomplishing so much with so much pressure is amazing.”

After reaching the finals of the USTA Girls Nationals in San Diego earlier in August, Hui was given a wild card into the women’s qualifying and lost to Genie Bouchard in round one, a defeat that Hui said gave her a lot of confidence heading into the juniors.

“I had such high expectations and put a lot of pressure on myself before playing Genie,” Hui said. “With this tournament I didn’t put a lot of pressure on myself, and I felt more ready.”

The girls' doubles champions were a team that was only playing its third tournament together. No. 8 seeds Mara Gae, from Romania, and Anastasiia Gureva, from Russia, recovered from being a set down and 1-3 in the second set to defeat Japan’s Sara Saito and Nanaka Sato, 1-6, 7-5, 10-8.

Each team won semi-finals earlier on Saturday before the rain and lightning delays.

“I was not expecting this at all, and when something like this happens when you don’t expect it, it’s even more amazing,” Gureva said.

“When we were down, we tried not to focus on the result itself but only on the tennis, and things got better and better,” Gae said. “We changed our way of thinking, being more focused on ourselves, and I thought we had nothing to lose.”

In the super tiebreak, Gae and Gureva jumped out to a 7-4 lead, but four quick points by Saito and Sato made it 8-7.

Gureva then hit two huge serves, resulting in a service winner and then an ace out wide in the deuce court, to give them match point.

Moments later, a backhand from the Japanese team flew long, and two singles players who only teamed up six months ago were Grand Slam champions.

“We were in a tournament together seeded first and second and I asked her ‘do you want to play doubles?’ and she said ‘yes of course!” Gureva said with a laugh. “And we hit it off so well, even though I’d never spoken to her before. Now we have each other and it’s so great.”