Sabalenka reaches US Open quarters

"I love matches like that, because it was really challenging, and going through tough challenges and overcoming those challenges, it definitely gives you strength and really strong belief that you can do it," Sabalenka said. "So these kind of matches is really, really, really like a boost of confidence.

"Sabalenka is vying to become just the third woman, after Chris Evert and Serena Williams, to win three straight US Open titles.

She'll have to lift the trophy just to have a chance of retaining her world number one ranking, and even if she does her time at the top could end in New York, where second-ranked Elena Rybakina needs only to reach the semis to be assured of ascending.

"I completely separate myself from that, because it's just guessing," Sabalenka said of the multiple number one scenarios -- which could also see third-ranked Jessica Pegula or even No. 4 Coco Gauff end the tournament at the top. "I'm just trying to bring my best tennis every time I'm competing out there and basically fight for it," she added.

Sabalenka needed all of her powers of concentration in her first career meeting with Townsend, the world's second-ranked doubles player who boasts formidable skills at the net as well as power from the baseline and a steely return game. The match opened with five breaks of serve before Sabalenka managed a comfortable hold for a 4-2 first-set lead.

She had double-faulted to hand Townsend a break in the second game and Townsend broke again in the fourth with a massive service return. But Sabalenka's sustained power and precision proved a little too much.

Townsend broke her as she served for the set at 5-2, but by the time the American managed a hold for 5-4 it was too late, and Sabalenka held serve for just the second time to pocket the set, saving a break point before putting it away with a trademark forehand winner. Challenging beginning"She was returning really well," Sabalenka said.

"She saw where I'm going. She was blocking really well. I guess playing doubles and mixed doubles really helped her to react on, like, heavy serve.

"That was really challenging beginning, but then I had to adjust my serve, the speed, the spin, bring the variety into my service games just so I keep her guessing. "The second set unfolded in more traditional style, neither player facing a break point through the first three games.

Sabalenka blinked first, smacking a forehand into the net to give Townsend a break point then offering up a weak second serve that Townsend punished with a return winner for a break and a 3-1 lead. Sabalenka immediately broke back, however, launching a run of five straight games to take the match.