New York,  Canadian teenager Leylah Fernandez staged a fine comeback to knock out former US Open champion Angelique Kerber of Germany, and reach the first Grand Slam quarterfinal of her career.

In a battle of left-handers, world No.73 Fernandez fought back from a set and a break down to stun No.16 seed and 2016 US Open winner Kerber, 4-6, 7-6(5), 6-2, in 2 hours and 15 minutes, one day before her 19th birthday on Sunday evening.

Fernandez had also knocked defending champion Naomi Osaka of Japan out of the draw with a come-from-behind victory in the third round. Her fourth-round match against Kerber was nearly a mirror image of the contest against Osaka, as the Canadian again fought her way through a second-set tiebreak before ousting the German.

Former world No.1 Kerber came into the match having won 17 of her last 19 matches, as she had pulled off a resurgent summer which included her first WTA singles title in three years in Bad Homburg and a run to the semifinals at Wimbledon.

But Fernandez, one of two 18-year-olds to have reached the Round of 16 this week (Emma Raducanu is the other), persevered through another comeback win in New York, smashing 45 winners past Kerber.

"The match was incredible," Fernandez said after her win. "I was playing well in the first set. Unfortunately I did a few mistakes. Her, as a great player, great champion, she noticed and she took advantage of it. I was able to refocus and fight back for the second. In the third, I was just enjoying every moment of it," Fernandez told wtatennis.com.

"At 3-4 [in the second set], I don't know if it was just a mindset or it was a feeling, but I just felt like that was the moment that I was going to break her serve and I was able to figure it out," said Fernandez. "I was just glad I was having fun on the court. I was trusting my game at 100 per cent."

"I have been working hard every day since the day I started playing tennis and since the day I set my mind to being a professional," Fernandez added. "I expected that one day my tennis game is going to come through and that I'm going to be on the big stage in front of a big crowd playing against big players and also getting the wins."

In the quarterfinals, Fernandez will take on No.5 seed Elina Svitolina of Ukraine. The 2019 US Open semifinalist, Svitolina dispatched No.12 seed Simona Halep of Romania 6-3, 6-3 in one hour and 16 minutes.

Fernandez and Svitolina have faced off once before, with Svitolina winning their quarterfinal clash in Monterrey last year.

No.2 seed Aryna Sabalenka of Belarus made it into her first US Open quarterfinal with ease, storming past her good friend, No.15 seed Elise Mertens of Belgium, 6-4, 6-1, in an hour and 10 minutes.

"I'm just really happy to be in the quarterfinals here because I really like playing at the US Open, especially with the crowd, and the atmosphere is really enjoyable here," Sabalenka said afterwards.

Sabalenka and Mertens have teamed up to win two Grand Slam doubles titles together, and each of them have taken a turn at doubles world No.1 during that run (Mertens currently still occupying the top spot in doubles).