It’s a birthday Leylah Fernandez will never forget…

The half-Ecuadorian Canadian tennis player, who just turned 19 on Monday, defeated No. 5 seed Elina Svitolina 6-3, 3-6, 7-6 (5) at the US Open to reach her first Grand Slam semifinal.

In the process, the unseeded Canadian teenager with an exciting game and enthusiasm to match became the youngest player to get that far in the women’s bracket at Flushing Meadows since Maria Sharapova.

Fernandez had previously recorded wins over past US Open champions Naomi Osaka and Angelique Kerber.

“I obviously have no idea what I’m feeling right now,” said Fernandez, a left-hander with quick baseline reflexes who is ranked 73rd and participating in only the seventh major tournament of her early career. “I was so nervous. I was trying to do what my coach told me to do.”

That coach is her father, who isn’t in New York; he stayed home and is offering tips in daily phone conversations. That helps, certainly, as does the loud backing she has been receiving from the spectators, who rose and cheered wildly each time Fernandez raised a fist high above her head or wind-milled both arms after winning a key point in Arthur Ashe Stadium.

“Thanks to you, I was able to push through today,” she told the crowd after edging Svitolina, the 2020 Tokyo Games bronze medalist whose two Grand Slam semifinal runs include the 2019 US Open.

Not requiring any encouragement to get out of his seat was Fernandez’s fitness coach, who would leap and shout, pointing fingers or waving clenched fists. Svitolina’s husband, two-time major semifinalist Gael Monfils, offered similar support from Ashe’s other guest box.

It was touch-and-go down the stretch — even after Fernandez grabbed the opening set, and even after she led 5-2 in the third. One way in which she held a clear advantage: Of points that lasted more than eight shots, Fernandez won 26, Svitolina 16.

Five times, Fernandez was two points from winning but failed to collect the next point. Finally, at 5-all in the tiebreaker, she moved to match point when she smacked a down-the-line passing shot that got past Svitolina with the help of a bounce off the net tape.

Fernandez put up both palms, as if to say, “Sorry about that bit of luck,” while Svitolina put a hand to her mouth in dismay.

Svitolina’s backhand contributed to her undoing late, and when a return from that side landed long, it was over. Fernandez dropped to her knees at the baseline and covered her face; Svitolina walked around the net to approach Fernandez for a hug.

Next on this magical ride for Fernandez will come yet another test against a player who is ranked higher and has more experience on the sport’s biggest stages: Aryna Sabalenka. Sabalenka, the No. 2 seed, matched her best result in a Grand Slam tournament by reaching the semifinals via a 6-1, 6-4 victory over French Open champion Barbora Krejcikova, who was seeded No. 8.