US Open champion Sloane Stephens kept alive her bid for back-to-back titles in New York, defeating former world No.1 Victoria Azarenka 6-3 6-4 in a gritty match to set up a fourth-round showdown with Elise Mertens.

The third-seeded American was the sharper of the pair at the outset on Friday, firing nine winners and fending off Azarenka’s lone break-point opportunity to take the first set in a little over half an hour.

But two-time Australian Open champion Azarenka raised her game in the second set, battling back from a 3-1 deficit to take a 4-3 lead, much to the chagrin of the partisan New York crowd.

A break in the action to close the roof on Arthur Ashe court appeared to bolster Stephens, who tightened up her defence and broke the big-serving Belarusian for a fifth time with a forehand winner to ward off the comeback and go through.

“When things got tough I hung in there,” Stephens, who is the highest remaining seed in the women’s draw, said in an on-court interview.

“You guys helped a lot,” she told the crowd.

A dejected Azarenka said she was disappointed with aspects of her performance.

“At this stage, it’s a matter of one, two points, and today I just need to cut down my unforced errors,” Azarenka told reporters.

“Those unforced errors that come out, right now they are costing me matches.”

Azarenka committed 27 unforced errors, while Stephens had 17.

“The fight was good throughout,” Stephens told reporters.

She acknowledged she was a “little rocky in the second set” but was satisfied to have “played a solid match”.

Stephens will look for redemption when she faces Mertens on Sunday after losing to the Belgian at the Cincinnati Masters earlier this month.