From a first lesson at The Park Club in Acton nine years ago, to the cusp of a Grand Slam championship.

That’s Mika Stojsavljevic’s path, as the 15-year-old keeps on making history for herself here at the US Open.

The hard-serving Brit, who still goes to in-person school at The Amherst School, continued her surprising dominance here Friday at the Billie Jean King National Tennis Center.

Unseeded and unheralded coming into the week, the 6-footer played “the best set of my life” in a 6-0 thrashing of No. 3 seeded American Iva Jovic in the girls semifinals, then steeled herself to score a third-set comeback in a 6-0, 3-6, 6-3 win that advanced Stojsavljevic to her first Grand Slam final here Saturday.

Stojsavljevic will be seeking to become the first British girl to win at the U.S. Open since Heather Watson in 2009, but she’ll be facing a player trying to make history herself.

Japan’s Wakana Sonobe, the No. 7 seed, had never been past the third round at a major but she continued her own fantastic week, knocking off British No. 8 seed Mingge Xu, 6-4, 6-4.

Sonobe will be trying to become the first Japanese girl to ever win a Junior Grand Slam title; in 2010 Sachie Ishizu reached the finals of Wimbledon before losing.

“It feels amazing,” Stojsavljevic said to a gaggle of reporters after the win. “I didn’t expect it but it feels great.”

Nine months ago Stojsavljevic faced Jovic and the result was very different; at the J300 Bradenton event, called the Eddie Herr, the 16-year-old American trounced Stojsavljevic, 6-3, 6-1.

“I think I had more clarity this time,” she said. “I trusted my game more, and my mindset wasn’t as cloudy.”

The first set was shockingly one-sided for the Brit; she made 13 winners, hit only six unforced errors and had a lead after only 19 minutes.

But Jovic, also a Wimbledon semi-finalist who reached the second round of the women’s draw, battled back, breaking serve in the fifth game as Stojsavljevic double faulted three times.

In the deciding set, Stojsavljevic broke at 2-all and then held her serve and her nerve, before playing a splendid final game, with two winners. When a Jovic short forehand sailed long, Stojsavljevic dropped her Yonex racket and ran over to hug LTA coach Katie O’Brien, her smile as wide as the East River here.

Shortly afterwards Sonobe took the court and as she’s been doing all week, she dominated. The 16-year-old from Saitama, Japan hasn’t lost a set in her five matches, and she quickly took advantage of Xu, who played four hours of tennis Friday between singles and doubles.

Sonobe, who has trained for the past 2.5 years at IMG Academy in Florida, grabbed a 2-0 lead in the second set before Xu battled back. But with Xu serving at 4-5, Sonobe pressed the action and grabbed the win on her first match point.

“I’m so happy and super excited for tomorrow,” Sonobe said. “I tried to be aggressive and tried to dominate the game. I tried to play a high-quality ball every time.”

Masahi Yoshikawa, one of Sonobe’s coaches, said his player’s tenacity has been special.

“She’s working every point, and her physical level is improved,” Yoshikawa said. “And mentally she’s been really strong, to keep doing what she wants to do. Her body is getting stronger so her shot has more consistency and is stable, with power and speed.”

Sonobe and Stojsavljevic have played twice competitively; at last year’s U.S. Open Stojsavljevic won a three-set battle, and at the 2023 Wimbledon the Brit also prevailed in three sets.

The girls doubles final is also set; Malak El Allami of Morocco and Emily Sartz-Lunde of Norway will square off with Julie Pastikova of Czechia and Julia Stusek of Germany.