Stan Wawrinka and Juan Martin Del Potro to meet in US Open quarter-finals

Stan Wawrinka and Juan Martin del Potro will meet in the quarter-finals of the US Open after contrasting fourth round successes.

Del Potro was handed an easy passage into the last-eight when Dominic Thiem retired from their encounter midway through the second set while trailing 6-3 3-2.

Wawrinka had things harder for a second successive match, dropping a set to unseeded Illya Marchenko two days after being taken the distance by Britain's Dan Evans.

The third seed looked to be in cruise control when he opened up a two-set lead for the loss of only five games, but he was sloppy in the third before regaining his rhythm to progress 6-4 6-1 6-7 6-3.

Things will get even tougher in the quarters for Wawrinka, despite Del Potro's lowly world ranking of 142.

"It's going to be great to play (Del Potro)," Wawrinka said. "He beat me this year at Wimbledon. He's back after so many injuries, so it's good to see him playing so well again.

"It's going to be a great challenge for me to play him here on the hard court for the first time. Excited to play against him and hopefully I can keep going here."

The Argentine has been in fantastic form since his long-awaited return from a series of wrist surgeries, giving Andy Murray an almighty scare when they met in the final of the Olympics in Rio last month.

Del Potro won the championship at Flushing Meadows in 2009 and looks to be heading back to that kind of form, albeit not needing to be at his best against a limping Thiem.

The Austrian blamed compensating for blisters on his feet for a problem with his knee that forced him to bring an end to the match after consulting with trainers.

"I was close to retiring before my third surgery but after that I always believe in myself to come back," said Del Potro,

"When I made the decision to do the surgery, I always believed I will come back, for sure. I didn't expect to be in quarters in my second grand slam after my comeback.

"My level is growing up every day. Everything can happen."

Sixth seed Kei Nishikori also made it through to the last-eight with a 6-3 6-4 7-6 win over big-serving Croat Ivo Karlovic and will next face Britain's Andy Murray.