NEW YORK, NY, USA -- No.15 seed Bianca Andreescu of Canada pulled off a stirring comeback victory on Wednesday night, overcoming No.25 seed Elise Mertens of Belgium, 3-6, 6-2, 6-3, to reach her first-ever Grand Slam semifinal in her US Open main-draw debut.

"It took a lot of hard work," Andreescu said in her post-match press conference. "The passion's always there, though. Even through the tough times I try to stay as optimistic as I can."

In the first meeting between the combatants, the 19-year-old from Ontario fought off a spirited Mertens in just over two hours of play, becoming the first teenager to reach the final four at the year’s final Grand Slam event since then-19-year-old Caroline Wozniacki advanced to the final of the 2009 edition.

"I think anyone would be shocked to be in the semifinals of a Grand Slam, because all of us dream of this moment ever since we're kids, ever since we picked up a racquet," Andreescu noted. "I definitely think that I have fought really hard to get to this point, so I think I do deserve to be here and hopefully I can go all the way."

It continues the searing run into the elite of women's tennis for Andreescu, who began the year outside the Top 100 before winning prestigious titles in Indian Wells and Toronto to burst into the Top 15. Andreescu is on an 11-match winning streak overall, dating back to her title run in her home country at the Rogers Cup last month.

"If someone told me that I was going to be in the semifinals of the US Open a year ago, I would say, 'You're crazy,'" Andreescu stated.

The rapidly rising Canadian teenager finished the match with 40 winners, outnumbering her 33 unforced errors. Despite only going 4-for-16 on break points, Andreescu was still able to get past Mertens, who could only break serve twice. The Belgian had pinpoint groundstroke accuracy in the first set but ended the clash with 27 unforced errors, compared to just 22 winners.

Andreescu scampered around the court in the first game to draw early errors from Mertens, earning two break points, but the Belgian stayed cool and collected to fend off those chances before knocking off a cluster of good serves to close out a service hold.

The steely early play by Mertens paid dividends when she clocked a backhand winner down the line to earn two break points of her own at 2-1, then fired a dipping backhand right at the feet of a net-rushing Andreescu to force a netted error and claim the first service break of the match.

Andreescu was in dire straits serving at 4-1 as well, when she had to summon some fierce forehand work to erase three break points and eke out a hold for 4-2. But Mertens was unfazed by the missed chances, and the Belgian’s groundstrokes were hitting small targets with precision. Serving for the set at 5-3, the Belgian fired an ace to hold serve at love for the one-set lead.

Andreescu, though, found her range in the second set. The players exchanged breaks early and Mertens used all-court play to stave off two break points before holding for 2-2 with a forehand winner down the line. The Canadian, however, used that same shot to reach a 3-2 lead, then broke the set open with a break at love, punctuated with a fiery forehand to force an error.

The forehand of Andreescu clicked at the end of the second stanza, as she hit two winners from that wing en route to a hold for 5-2. The Canadian wrapped up the set with another break for good measure, firing a final forehand winner, this one crosscourt, to level the match at one set apiece.

The players had a matching ten unforced errors in the second set, but Andreescu out-winnered Mertens by 14 to four. That was a far cry from the opening set, where Mertens had 12 winners to nine unforced errors, and Andreescu’s 11 winners were undone by 14 miscues.

"I just told myself to keep fighting and hope that I can switch things around basically," Andreescu said, explaining her mentality which turned the match around after losing the opener. "I tried to stay more aggressive than the first set, and I felt like I was missing a lot in the first set, as well."

"I saw that [Mertens] was picking on my backhand a lot, so I tried to go more down the line with my backhand so she can go back to my forehand, so I can use my forehand, because I like my forehand," Andreescu continued, with a smile. "She executed some good tactics in the first set. I just told myself to just keep fighting and to not give up. That was the main thing."

Andreescu made it through the entire third set without facing a break point, while the Mertens service games had become far more complicated, but the Belgian continued to stay even-keeled, fending off the first six Andreescu break points of the decider.

But the Canadian converted lucky number seven, cracking a monstrous backhand service return which Mertens clipped with her racquet, catching the net and giving Andreescu the first and decisive break of the set to lead 5-3. In the next game, Andreescu hit one final backhand winner to wrap up the victory and complete the singles semifinal lineup.

Andreescu will now face fellow first-time Grand Slam semifinalist and No.13 seed Belinda Bencic of Switzerland in the final four, with the winner to contest her first-ever Grand Slam final. Bencic booked her spot in the semifinals earlier on Wednesday with a straight-set victory over No.23 seed Donna Vekic of Croatia. It will be the first meeting between Andreescu and Bencic.

"I have practiced with [Bencic] once, actually in Toronto," said Andreescu. "I found that she takes the ball really early. She likes to be very aggressive. She has a very good serve. She moves pretty well, too. So I'm going to do my best to just focus on myself mainly and just keep doing what I'm doing, because I think my game is throwing off a lot of players."

"At this point I think anyone can win the tournament," Andreescu stated. "The other semifinalists are incredible athletes, tennis players. So I know it's not going to be easy tomorrow, and if I win tomorrow, in the finals, as well. So I'm just going to take in this moment now."