Stephens survives Azarenka test

Defending champion Sloane Stephens reached the US Open fourth round on Friday, winning the last three games in a straight-sets victory over Victoria Azarenka after a brief break to close the Arthur Ashe Stadium roof.

Up a break in the final set, Stephens had slipped behind 4-3 when a light shower prompted officials to close the roof for the first time this week.

Both players had a chance to leave the court and the break refreshed Stephens.

"I changed my dress and I was, like, 'All right, keep fighting, keep playing. That was pretty much it," she said. "I won the next three games. I played some really good points those games. I was happy with that.

"I don't think it was so much the roof closing, but more just kind of refocusing," added Stephens, the third seed who is the highest ranked woman left in the field after early exits for world number one and two Simona Halep and Caroline Wozniacki.

Stephens knew that former world number one Azarenka, a two-time Australian Open winner and a two-time finalist at Flushing Meadows, would be a dangerous opponent.

But the Belarusian, working her way back towards the top after time off to have a child, said she still isn't sharp enough when it matters most.

Stephens got the ball rolling on Ashe on a day when the 30th career meeting between Serena and Venus Williams was the main attraction.

Both sisters admit it's not a match-up they relish.

"I wouldn't say it's exciting," Serena said. "It's definitely going to be a really tough match for me.

"The best part is we bring out the best in each other," Serena said. "I know when I play her I have to play some of my best tennis. She does, too. It sets a tone for us."

Venus's seven Grand Slam titles include a victory over Serena in the 2001 US Open final. But Serena has gone on to beat her elder sister in seven of eight major finals since on her way to 23 Grand Slam titles.

That's an Open Era record, and with one more she'll match the all-time record 24 of Australian Margaret Court.

In other early matches, 15th-seeded Belgian Elise Mertens defeated Czech Barbora Strycova 6-3, 7-6 (7/4) to set up a clash with Stephens.

Seventh seeded Ukrainian Elina Svitolina beat China's Wang Qiang 6-4, 6-4 and will fight for a quarter-final berth against Latvian Anastasija Sevastova, a 4-6, 6-1, 6-2 winner over Russian Ekaterina Makarova.