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. After she recovered from that to take a lead, 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. 

And why would she at this point? The Canadian's poise, it seems, is as limitless has 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 right to play for a Grand Slam title.

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 Sabalenka.

In Saturday's final, the left-handed Fernandez will face either another unseeded teen, 18-year-old qualifier Emma Raducanu of Britain, or 17th-seeded Maria Sakkari of Greece. Neither of them has participated in a Grand Slam title match, either.

In the end, 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.