NEW YORK • It was way back in March, before Bianca Andreescu had ever won a WTA title, when she lost in the semi-finals of a tournament in Acapulco, Mexico.

That was the last time the 19-year-old Canadian finished a match on the wrong side.

Six months and two titles later, that is the way the 15th seed rolls into the US Open final against Serena Williams today with a chance to win her maiden Grand Slam title.

"Hopefully I can just keep the momentum going for the finals," said Andreescu, who is playing at just her fourth Slam and making her US Open main-draw debut.

She is 33-4 this season after beating world No. 12 Belinda Bencic of Switzerland 7-6 (7-3), 7-5 in Thursday's semi-finals.

She is the first Canadian in a Slam final since Eugenie Bouchard at Wimbledon in 2014, and the first teenager to play for the US Open title since Caroline Wozniacki did it a decade ago.

She owned just two Slam main-draw victories coming into Flushing Meadows, and had lost in the first round of qualifying the past two years.

"I wasn't going through a good period in my life at that point," she said, referring to a first-round loss to Olga Danilovic in 2018 qualifying. "I was having problems with some relationships in my life, with my body, and even my mind, too.

"But I'm glad I went through it because at one point you have to. I think I just learnt a lot."

She seemed headed to a third set on Thursday when she fell behind 5-2 in the second. But she did not drop another game from there, saying she believes her best tennis comes out when she is down, just like her lessons in life.

"I think it's just inside of me somehow," she said. "I think it's just my passion for the game as well. I don't like to lose."

She almost never does.

Andreescu followed her semi-final loss to Sofia Kenin in Mexico on March 1 by making her first title a top-tier one, becoming the first wild card to win at Indian Wells later that month.

She then went to Miami and had to stop in her fourth-round match with a right-shoulder injury, officially her last loss.

She was out until the French Open in May, won her first match before having to withdraw ahead of her second-round match, again because of the shoulder.

That forced her to miss the entire grass-court season before coming back last month in Toronto, where she won the title when Williams had to retire in the final because of back spasms.

Now, the world No. 15, who has enjoyed a rapid rise after finishing 2018 ranked 178th, is eagerly awaiting the showdown with 23-time Slam singles champion Williams.

"I've wanted to play her. I remember always telling my team I always wanted to play her right before she retires," said Andreescu, who was not even born when Williams, 37 and nearly twice her age, won her first major title at the 1999 US Open.

"I'm really looking forward to it. She's an amazing champion on and off the court. It's going to be fun.

"Hopefully I can play better than I did (against Bencic).

"If someone told me a year ago I would be in the US Open final this year, I'd tell them they were crazy."

ASSOCIATED PRESS, AGENCE FRANCE-PRESSE