Defending US Open champion Sloane Stephens kept alive her bid for back-to-back titles in New York, defeating former world number one 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.

Stephens will look for redemption when she faces Mertens on Sunday after losing to the Belgian in straight sets at the Cincinnati Masters two weeks ago.