Hitting sublime backhands, defending champion Stan Wawrinka surged 7-6 (5), 6-7 (7), 6-3, 6-2 into the French Open quarterfinals, so in control against Viktor Troicki on Sunday that he amused himself and the crowd by hitting with a ball boy while the Serb took time out for treatment in the third set.

After lending the lucky lad a racket for their impromptu hit-about, the third-seeded Swiss got back to business, securing his win in cold and humid conditions on Court Philippe Chatrier in just under three hours. Also through to the quarters: second-seeded Andy Murray, in a rain-interrupted 7-6 (9), 6-4, 6-3 victory over big-serving American John Isner.

Wawrinka needed eight set points to overcome Troicki, seeded No. 22, in the first set. He failed to capitalize on the first four when Troicki was serving at 5-6 and then saw three more go to waste in the tiebreaker before getting the set lead in 49 minutes.

In the second tiebreaker, it was Troicki who needed five set points to break down Wawrinka, who hit an attempted forehand lob long for the Serb to level.

A backhand winner from Wawrinka — one of 14 from him in the match — broke Troicki to love in the fourth game of the third set, during which the Serb got treatment on his right leg and was given pills and Wawrinka made the ball-boy's day.

"I was a little bit bored, was waiting for him, was talking to the ball kid," Wawrinka said. "I asked him if he was playing tennis. I said, 'OK, let's play.'"

Wawrinka staved off a break point with a sublime cross-court backhand for a 5-1 lead in the fourth set. An ace brought up two match points for Wawrinka and he converted the first when Troicki netted a backhand from the baseline.

Garbine Muguruza also advanced to the quarterfinals for a third straight year. The array of shots and maturity the 22-year-old deployed in an intensely fought 6-3, 6-4 win against 2009 champion Svetlana Kuznetsova strengthened the argument that Muguruza could soon be challenging Serena Williams for the top spot in women's tennis.

The fourth-seeded Spanish player started at lightning pace, serving an ace with her first and third balls. In the last game, she stayed cool during five match points to finish off the 13th-seeded Russian.

Standing in the way of her second semifinal at a major tournament is Shelby Rogers. The 108th-ranked American who had never made it out of the third round at one of the Grand Slams beat Irina-Camelia Begu 6-3, 6-4. The Romanian, seeded No. 25, is the third seeded player to fall to Shelby in her march to the quarterfinals.

"I'm definitely outside of my comfort zone already, and I keep telling myself, 'You belong here, you belong here,'" Shelby said.

Albert Ramos-Vinolas, a 55th-ranked Spanish player who had never made it past the second round of 18 previous Grand Slam tournaments, also is on a roll. He ousted Milos Raonic 6-2, 6-4, 6-4 — breaking the eighth-seeded Canadian five times and saving six of seven break points — to play Wawrinka in the quarterfinals.

"I have no words to explain how I feel," Ramos-Vinolas said. "It was four years in a row losing in the first round."

Cool and cloudy weather appeared to take some bite out of Raonic's serve on the red clay, with new coach John McEnroe among the spectators on Court Suzanne Lenglen before they work together at Wimbledon next month. Raonic, a quarterfinalist at Roland Garros in 2014 and semifinalist at this year's Australian Open, complained of an aching left hip in his previous match but didn't appear to have trouble moving against Ramos-Vinolas and later said it wasn't an issue.

Raonic beckoned over the chair umpire in the last game to inspect a shot that gave Ramos-Vinolas two match points. She ruled it in, pointing that the ball had nicked the line.

The Spaniard couldn't capitalize on those opportunities. But he made no mistake with his third match point, earned with an ace served out wide, sealing the win in 2 hours and 20 minutes with a smash.

He celebrated by firing a spare ball into the air in delight.