Rome - Monte Carlo champion Stanislas Wawrinka has joined fellow Swiss Roger Federer on the scrapheap at the ATP-WTA Rome Masters on Thursday as back pain resulted in a 5-7, 6-2, 6-3 loss to 15th seed Tommy Haas.
The 36-year-old has now won both of his matches with Wawrinka, a 2008 finalist at the Foro Italico.
Andy Murray, who quit the event with back problems a year ago and eventually required surgery, closed out a welcome win over Jurgen Melzer with his sixth ace for a 7-6 (7/1), 6-4 result which puts him into his second straight clay quarter-final after Madrid a week ago.
Germany's Haas ended with seven aces to eight for Wawrinka, who could not hold onto leads throughout the two-hour contest. The winner produced 32 winners while Wawrinka struck 40 unforced errors.
Haas broke in the third set for 5-3, then finished with an ace a game later on his first match point.
Wawrinka said that after playing a match in the chill two days earlier, he started having back problems.
But experience told him that he worry is not serious and should not affect his chances for Roland Garros starting in 10 days.
"It was difficult to give the intensity. I know my back, I just need some rest - maybe two days is enough - But I'm not worried about it," he said.
"I played because I wanted to try. It was not easy to put all energy onto my game. I won first set even if I was not playing my best.
"Even though, I still thought I had a chance to win it. He was more aggressive in the second set and was doing more things on the court."
Murray now owns a perfect 7-0 record over Austrian Melzer, who is back on court after shoulder problems,
The winner spent just under one and three-quarter hours on the clay as his confidence on his least favourite surface starts to improve.
Canadian eighth seed Milos Raonic reached his first Rome quarter-final with a defeat of French 11th seed Jo-Wilfried Tsonga 7-6 (7/5), 6-4. Jeremy Chardy, who beat Federer 24 hours earlier, kept up his momentum by defeating Ivan Dodig 6-3, 6-2.
In women's play, Chinese second seed Li Na defeated Samantha Stosur 6-3, 6-1 to reach the quarter-finals, turning the momentum in a long-running rivallry.
Stosur, a 2010 Roland Garros finalist, had beaten world number two Li in all six of their previous meetings going back to 2007.
The victory was her second straight over an Aussie opponent after defeating qualifier Casey Dellacqua in the previous round.
But China's top female athlete made inroads against Stosur's one-way scoreline with her first victory, achieved in 68 minutes with five breaks of the 30-year-old Australian.
"Today I was very focused on what I had to do on the court to put pressure on her," said Li. "Putting on pressure was the key to the match, otherwise she can totally control you.
"I now feel I'm playing high quality matches."
Li will play a quarter-final against Italian tenth seed Sara Errani, who beat Czech Petra Cetkovska 6-3, 7-6 (7/3).
Li finished Rome runner-up in 2012, holding a match point against eventual champion Maria Sharapova.
Australian Open champion Li is looking for her third trophy of the season as she prepares for the French Open, which she won in 2011.
Third-seeded Pols Agnieszka Radwanska put out Italian veteran Francesca Schiavone, the 2010 French Open winner, 6-4, 6-1.
Ana Ivanovic handed Maria Sharapova her first loss of the spring clay season as she beat the Russian eighth seed 6-1, 6-4.
Sharapova had won back-to-back titles in Stuttgart and Madrid, compiling a dozen straight victories.
Ivanovic, the 2008 Roland Garros winner and world number one, had won just two of 10 previous meetings with the four-time grand slam champion, the last seven years ago at a Roland Garros semi-final.
Results on Thursday from the fourth day of the WTA/ATP Rome Masters tournament: -
Carla Surez Navarro (ESP x13) bt Simona Halep (ROM x4) walkover
Sara Errani (ITA x10) bt Petra Cetkovsk (CZE) 6-4, 7-6 (7/3)
Li Na (CHN x2) bt Samantha Stosur (AUS) 6-3, 6-1
Ana Ivanovic (SRB x11) bt Maria Sharapova (RUS x8) 6-1, 6-4
Tommy Haas (GER x15) bt Stanislas Wawrinka (SUI x3) 5-7, 6-2, 6-3
Milos Raonic (CAN x8) bt Jo-Wilfried Tsonga (FRA x11) 7-6 (7/5), 6-4
Jeremy Chardy (FRA) bt Ivan Dodig (CRO) 6-3, 6-2
Andy Murray (GBR x7) bt Jurgen Melzer (AUT) 7-6 (7/1), 6-4