US Open: Angelique Kerber and Caroline Wozniacki win first-round US Open ties

Second seed Angelique Kerber enjoyed a stress-free passage into the US Open second round after her opponent Polona Hercog retired injured.

Kerber, the reigning Australian Open champion, whitewashed the first set 6-0 before world No 120 Hercog quit after losing the opening game of the second set. Hercog had won just nine points in seven games.

Caroline Wozniacki won her first Grand Slam match of 2016 with a 4-6 6-3 6-4 win over qualifier Taylor Townsend. The former world No 1 had suffered first-round exits at the Australian Open and Wimbledon, and missed the French Open with injury.

Third seed Garbine Muguruza came from a set behind to eliminate Elise Mertens  2-6 6-0 6-3.

Muguruza had to call for the doctor after losing the opening set, complaining she was struggling to breathe, but she rallied after the time-out and eventually found her form with a vengeance.

Roberta Vinci, who eliminated Serena Williams at last year's US Open, also cruised into the second round.

World No 8 Vinci lost the 2015 final to Flavia Pennetta but returned on-song with a 6-2 6-4 win against Anna-Lena Friedsam.

Petra Kvitova, the 14th seed, won 7-5 6-3 against Jelena Ostapenko while 24th seed Belinda Bencic eliminated Samantha Crawford with a 6-7 6-3 6-4 win.

But the Olympic champion and 32nd seed Monica Puig is out, defeated 6-4 6-2 by China's Zheng Saisai.