
Roberta Vinci moved a step closer to another final at the US Open by beating Carina Witthoeft.

Vinci, who stunned Serena Williams last year, won 6-0 5-7 6-3 to reach round four.

Comeback of the day went to Madison Keys. She trailed 5-1 in the third before defeating Naomi Osaka 7-5 4-6 7-6 (7-3).

Two-time US Open finalist Caroline Wozniacki -- who meets Keys next -- followed up her upset win over Svetlana Kuznetsova by defeating Monica Niculescu 6-3 6-1.

Novak Djokovic got more good luck when his opponent, Mikhail Youzhny, retired trailing 4-2 in the first set.

Djokovic -- the world No. 1 -- didn't have to play in the second round because of an injury to opponent Jiri Vesely.

Jack Sock took out 2014 winner Marin Cilic 6-4 6-3 6-3, two weeks after Cilic won the prestigious Cincinnati Masters.

Jo-Wilfried Tsonga moved on by winning against an ailing Kevin Anderson 6-3 6-4 7-6 (7-4). Anderson upset Andy Murray last year in New York.