US Open: Madison Keys locks up last-16 spot

Madison Keys, vying to return to the US Open final, was back in the last 16 after a 4-6, 6-1, 6-2 victory over Aleksandra Krunic.

Madison Keys celebrates after beating Aleksandra Krunic of Serbia.   -  AFP

Madison Keys, vying to return to the US Open final, was back in the last 16 after a 4-6, 6-1, 6-2 victory over Aleksandra Krunic on Saturday. Keys, the 14th seed, sounded a little relieved after surviving an error-strewn performance to improve to 4-0 in US Open third-round matches.

“I was definitely a little nervous and she came out playing really well and put a lot of pressure on me from the start,” said Keys, whose pre-match aim of getting comfortable on Arthur Ashe Stadium “clearly didn't happen.”

“I'm happy to be in the next round,” said the 23-year-old American who will face either Wimbledon champion Angelique Kerber or Slovakian Dominika Cibulkova for a place in the quarterfinals.

The match was the curtain raiser to five-time champion Roger Federer's third-round duel with Australian Nick Kyrgios.

It's a potentially tough match-up for the second-seeded Swiss. He's won two of his three meetings with the unpredictable Aussie, but all three matches have gone the distance and eight of nine sets they've played have gone to tiebreakers.

The winner of the match will face Australian John Millman, who reached the US Open last 16 for the first time with a 6-4, 4-6, 6-1, 6-3 victory over Kazakhstan's Mikhail Kukushkin.

Wimbledon champion Novak Djokovic headlines the evening action on Ashe against French veteran Richard Gasquet.

Djokovic beset by injury and self-doubt to start the season, broke out of the doldrums with his 13th Grand Slam title at the All-England Club.

He promptly backed that up with a Cincinnati Masters title to confirm he's a legitimate challenger to Federer and world number one Rafael Nadal despite his relatively modest sixth seeding.

Former champion Maria Sharapova is also in action on Ashe, taking on former French Open champion Jelena Ostapenko of Latvia for a place in the last 16.

In early results, 19-year-old Czech Marketa Vondrousova won a roller-coaster battle against 13th-seeded Kiki Bertens of the Netherlands 7-6 (7/4), 2-6, 7-6 (7/1) to continue her best ever Grand Slam showing.