SYDNEY (Reuters) - Garbine Muguruza’s preparations for next week’s Australian Open were thrown into disarray when the world number three pulled out of the Sydney International with a thigh injury on Wednesday. Hours after battling past Kiki Bertens 6-3 7-6(6) to advance to the quarter-finals, the 24-year-old Spanish top seed withdrew with a right thigh injury. The Wimbledon champion accepted a wildcard into the tournament after retiring with leg cramps during her opening match at the Brisbane International last week and called for a medical time-out after the third game against Bertens. Muguruza, however, returned to the Ken Rosewall Arena in full flow, breaking her Dutch opponent twice to surge 5-1 clear, apparently allaying fears of another injury setback ahead of next week’s Australian Open. Bertens, who had won all three previous meetings against Muguruza in straight sets, recovered one of the breaks to halt her opponent’s march but the twice grand slam winner regrouped to close out the opening set. Muguruza broke at the start of the second set against the 26-year-old world number 32 but struggled to impose herself during the key moments, only converting three of 13 break-point opportunities and dropping her serve in the eighth game. She rallied, however, to seal victory on her fourth match point in the tiebreak when Mertens hit a return long. “Since the start I felt a little bit my adductor,” Muguruza said after registering her first win of the season. ”I already felt it in Brisbane, so I thought I was going to be much better, but it came back. ”You always have to adapt... Sometimes you don’t need to have a pain. You just want to play a certain style of game or some tactic. “I figured out that being a little bit more aggressive, shorter points, that might help me and might help me also for my game. So it’s like a winning situation.” Agnieszka Radwanska, the 2013 champion and last year’s finalist in Sydney, kept her preparations for the year’s first grand slam on course with a 7-6(4) 6-0 win over teenage American qualifier CiCi Bellis. The Polish 28-year-old will meet Camila Giorgi for a place in the last four after the Italian qualifier ousted twice Wimbledon and former Sydney champion Petra Kvitova 7-6(7) 6-2. Giorgi, belying her ranking of 100th in the world, beat US Open champion Sloane Stephens in the first round and added another grand slam champion to her list of victims in just under two hours when Kvitova blasted a forehand wide. In the men’s draw, Italian veteran Paolo Lorenzi ousted top seed Albert Ramos-Vinolas of Spain in the second round. Ramos-Vinolas needed treatment for a leg problem early in the second set and fell 6-3 7-5 to the 36-year-old Lorenzi, who is ranked 45 in the world.