"I think it was a good match, in general, for sure. A few up-and-downs with focus and my (shot) choice during the game, but it's always tough to play against Troicki." Troicki was serving for the first set at 5-4 when Wawrinka scripted a turnaround to claim it. The three-times grand-slam champion took charge in the second when Troicki double-faulted at 4-4 and he clinched the contest to set up a quarter-final clash with Briton Kyle Edmund.
Third seed Kei Nishikori had to work harder to secure his quarter-final berth with a 4-6 6-4 6-3 win over free-swinging American Jared Donaldson.
Nishikori was 4-0 up and yet lost the first set as Donaldson reeled off six games on the trot. Nishikori let a 3-0 lead slip in the second as well but the 2014 US Open finalist managed to arrest the slide to force the decider and was more assertive in the third set against the 105th-ranked qualifier. "I had a great start today until 4-0, and then I had one bad game," Nishikori said.
"He started playing more aggressive and his forehand was on fire - he was hitting a lot of winners from that side." Nishikori now meets Australian Jordan Thompson who upset eighth seed David Ferrer 4-6 7-5 7-5 for the biggest win of his career to reach his first ATP World Tour quarter-final.