New York, Sep 4 : Canada's Leylah Fernandez, ranked 73rd in the world, accounted for one of the biggest seeds in the first week of the US Open, defeating No.3 Naomi Osaka of Japan 5-7, 7-6(2), 6-3 to end the 2020 champion's title defence in the third round. The win is the 18-year-old's second top-5 win of her career and puts her into her first Round of 16 at a Slam, where she will face 2016 US Open champion Angelique Kerber of Germany. Fernandez is a former junior champion at 2019 French Open who made her top-100 debut a year ago after the US Open. A left-hander who chose tennis over football, Fernandez won her first WTA title earlier this season on the hardcourts of Monterrey. Since that triumph in March, Fernandez had not won back-to-back main draw matches until her first two rounds in New York. Osaka received a walkover into the third round after Serbia's Olga Danilovic withdrew ahead of their second-round match on September 1. Riding a 16-match winning streak at the Slams, which dates back to her triumph here last year, Osaka started the match sharply, particularly on her serve, which did not face a break point in the first set. After the pair held serve for 10 games, Osaka reeled off the last nine points of the opening set to take it 7-5. "I was very happy how I played in the first set," Fernandez said. "I was serving well. I was playing well. She just edged up near the end. In the break I was telling myself to stay positive, keep fighting. I'm there, I'm close. "In the second set, I guess on the very last game I found the solution to the problem of returning her serve. I'm glad that I found it. I don't think I won more than two points on the return up until that game. I was trying to find different looks. I started off really far from the line. Then I was just edging closer and closer. Finally, I found a pattern to her serve. I just trusted my gut and hit the ball," Fernandez told wtatennis.com. Rattled by the abrupt turn of events, Osaka played an error-filled tiebreak to quickly fall behind 5-0 and Fernandez closed out a 7-2 tiebreak with a first serve wide that Osaka could not control. Fernandez took her momentum into the third set and immediately broke Osaka for a 2-0 lead. "From a very young age, I knew I was able to beat anyone, anyone who is in front of me," Fernandez said. "Even playing different sports, I was always that competitive, saying I'm going to win against them, I'm going to win against my dad in soccer, even though that's like impossible. I've always had that belief. I've always, like, tried to use that in every match that I go on. I guess today that belief came true." Fernandez will face No.17 Kerber for a spot in the quarterfinals. The German came through a tough three-set battle with 2017 champion Sloane Stephens earlier in the day, coming back to win 5-7, 6-2, 6-3. It will be the first meeting between the two. No.15 seed Elise Mertens of Belgium played a disciplined match to defeat No.20 seed Ons Jabeur of Tunisia 6-3, 7-5 to advance to her fourth consecutive Round of 16 in New York. The Belgian hit just six unforced errors off the ground for the match to end Jabeur's challenge in 1 hour and 28 minutes. Mertens will face either her friend and former doubles partner, No.2 Aryna Sabalenka, or San Jose champion Danielle Collins in the Round of 16. /IANS