Stan, Andy into last 16

Men's contenders Andy Murray and Stan Wawrinka clawed their way into the last 16 of the US Open en route to the US Open on Sunday.

While Serena Williams had encountered little resistance on way to her 307th win the day before, it was another story for the top men's seeds in action.

Wawrinka had the closest call, saving a match point in a 4-6, 6-3, 6-7 (6/8), 7-6 (10/8), 6-2 victory over Britain's Dan Evans.

The 31-year-old third seed saved the match point at 5/6 in the fourth set tiebreaker, breaking the will of his opponent.

"It's always good to win by saving match point. It's always something special, that's for sure," said Wawrinka, who had his left ankle taped after twisting it during the match. "It was a tough battle and I'm happy to get through."

Many of Murray's troubles against Paolo Lorenzi were of his own making as he allowed the energetic Italian journeyman to make him look ordinary through two sets before pulling himself together to win 7-6 (7/4), 5-7, 6-2, 6-3.

Murray takes on Bulgarian Grigor Dimitrov, a 6-4, 6-1, 3-6, 6-2 winner over Portugal's Joao Sousa, for a quarter-final berth.

Wawrinka next faces 63rd-ranked Ukrainian Illya Marchenko, who advanced when Nick Kyrgios, hobbled by a painful right hip, retired while trailing 4-6, 6-4, 6-1.

Kyrgios soldiered on after receiving treatment at the end of the second set before opting out at the end of the third.

Sixth-seeded Kei Nishikori of Japan, two years removed from his run to the final, rallied for a 4-6, 6-1, 6-2, 6-2 win over France's Nicolas Mahut.

Nishikoriwill take on Ivo Karlovic for a quarterfinal berth.