ROME - Rafael Nadal continued to search for his best clay form, surviving a shaky start on Thursday to reach the quarter-finals of the ATP-WTA Rome Masters and a date with Andy Murray.The top seed beat Russian Mikhail Youzhny, winning 12 of the last 13 games in a 6-7 (4/7), 6-2, 6-3 win which took almost three hours. Murray and Nadal have not played each other for more than two and a half years, when Murray beat the Spaniard in a 2011 Tokyo final. Less than 24 hours after being severely tested by Gilles Simon, Nadal found himself in trouble against Youzhny, who last won a set against the world number one back in 2008. After spending 73 minutes in losing the opener, Nadal finally found enough form to take the victory at a tournament where he is looking to win for the eighth time.Murray, who quit here with back problems a year ago and eventually required surgery, closed out a welcome win on his 27th birthday with an ace against Jurgen Melzer. The Scot won 7-6 (7/1), 6-4 to advance to his second straight clay quarter-final after Madrid a week ago, spending just under one and three-quarter hours on the clay as his confidence on his least favourite surface starts to improve. However, that confidence will be severely tested by Nadal.Meanwhile, Monte Carlo champion Stanislas Wawrinka joined fellow Swiss Roger Federer on the scrapheap 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. Germany's Haas ended with seven aces to eight for Wawrinka, who could not hold onto leads throughout the two-hour contest. Haas produced 32 winners while Wawrinka struck 40 unforced errors.Haas broke in the third set to lead 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 the worry is not serious and should not affect his chances for Roland Garros, starting in 10 days time."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 the first set even if I was not playing my best."Grigor Dimitrov beat sixth seed Tomas Berdych 6-7 (3/7), 6-2, 6-2 while 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 2010 French Open finalist Samantha Stosur 6-3, 6-1 to reach the quarter-finals."Today I was very focused on what I had to do on the court to put pressure on her," said Li, who won in 68 minutes with five breaks of the 30-year-old Australian. "Putting on pressure was the key to the match, otherwise she can totally control you." Li, runner-up in Rome in 2012, will next face Italian 10th seed Sara Errani, who beat Czech Petra Cetkovska 6-3, 7-6 (7/3).Third-seeded Agnieszka Radwanska put out Italian veteran Francesca Schiavone, the 2010 French Open winner, 6-4, 6-1, while sixth seed Jelena Jankovic beat Flavia Pennetta 6-2, 6-3 and 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. "I wasn't sharp today but Ana played well," said Sharapova. "I'm going to try to recover the next two or three days, settle down in Paris and get my body ready for a week of training."