NEW YORK — Leylah Fernandez‘s first major semifinal, at the US Open just days after her 19th birthday, did not go her way at the start.

She recovered from dropping the initial three games to take a lead, before No. 2 seed Aryna Sabalenka pushed a match filled with momentum swings to a back-and-forth third set. No matter what, Fernandez did not worry. Didn’t waver.

And why would she at this point? The Canadian’s poise, it seems, is as limitless as her potential. And no foe, no matter how accomplished or highly ranked, poses an insurmountable problem. Speedy afoot and steady at crunch time, the unseeded Fernandez edged Sabalenka 7-6 (3), 4-6, 6-4 on Thursday night in Arthur Ashe Stadium, earning the right to play for a Grand Slam title.

Her opponent: 18-year-old qualifier Emma Raducanu of Britain, who defeated 17th-seeded Maria Sakkari of Greece 6-1, 6-4 in the second semifinal to set up an all-teenager US Open women’s final.

Raducanu became the first player to come through qualifying to reach a Grand Slam final in the professional era. If Raducanu wins, she will be the youngest Grand Slam champion since Maria Sharapova won Wimbledon in 2004 at age 17.

It was the 73rd-ranked Fernandez’s fourth consecutive three-set victory over a seeded opponent. First came No. 3 Naomi Osaka, the 2018 and 2020 US Open champion. Then came No. 16 Angelique Kerber, the 2016 champ. That was followed by No. 5 Elina Svitolina and then Sabalenka.

“That’s years and years and years of hard work and tears and blood,” said Fernandez, who could give Canada its second US Open women’s title in three years, following Bianca Andreescu‘s triumph in 2019. “Everything. On court, off court. Sacrifices.”

Fernandez was born in Montreal to an Ecuadorian father — who is also her coach, although he is not with her in New York, instead offering coaching tips in daily phone conversations — and a Filipino Canadian mother. The family now lives in Florida.

At the end of the first set and again in the third, it was Sabalenka, a Wimbledon semifinalist in July, who let things get away from her. In the last game, she double-faulted twice in a row to set up match point, then sailed a forehand long.

Fernandez collapsed to the court and put her hands to her face.

Nearly 2½ hours before that, it was Sabalenka who looked in control, claiming 12 of the first 14 points for a 3-0 lead. Just eight minutes had elapsed and most spectators were yet to reach their seats. Not until later did the 20,000-plus in the stands rally the fist-aloft Fernandez with chants of “Let’s go, Leylah! Let’s go!” accompanied by rhythmic clapping.

Sabalenka tried at times to get them on her side, waving her arms to ask for some support, too.

She showed nary a hint of hesitancy. Truly not a trace of nuance, either. Her game is built on power with a purpose. Full speed ahead, always. Serves at up to 120 mph. Groundstrokes generated with full force.

And most swings of her racket announced with a loud grunt, winners noted with a shaking fist.

Fernandez got herself going eventually, as anyone who has watched her play over the past two weeks might have expected.

Her style is all about reflexes and court coverage, reaching everything and immediately redirecting balls back over the net, although she did produce one early love hold that featured a trio of aces and a service winner, albeit much slower than Sabalenka’s deliveries.

Fernandez went from 4-1 down to 4-all in a blink. Sabalenka came within a point of taking that set, leading 6-5 while Fernandez served at 30-40. But that chance was wasted when a forehand found the net.

In the tiebreaker, Sabalenka went up 2-0 and then completely lost her way.

“I wouldn’t say that she did something,” Sabalenka said. “I would say that I [destroyed] myself.”

Every point won by Fernandez came courtesy of a miss by Sabalenka, including a flubbed overhead that landed several feet long and a double-fault to hand over a set point. A backhand return into the net — Sabalenka’s fourth miss when replying to a second serve in the tiebreaker — ended that set to roars from the crowd.

“This,” Sabalenka said, “is what we call pressure.”

It was the sort of lapse that contributed to Sabalenka never getting past the fourth round in her first 15 Grand Slam appearances, until a breakthrough run to the Wimbledon semifinals.

In the second set, Sabalenka regained her form and Fernandez took a step back. Fernandez was two games from victory, serving at 4-all in the second, when she sailed a backhand beyond the baseline to get broken. Sabalenka held at love, and on to a third set they went.

And that, of course, was Fernandez’s time to shine. This is only her seventh Grand Slam appearance.

“Now she’s like [a] top-10 player,” Sabalenka said. “We’ll see how good she will be in the future.”

The Associated Press contributed to this report.