Agnieszka Radwanska, Li Na through to third round at US Open Agnieszka Radwanska returns a shot to Maria-Teresa Torro-Flor during their second round match at the 2013 US Open in Queens, New York. AGNIESZKA Radwanska and Li Na reached the US Open third round on Wednesday as defending men's champion Andy Murray impatiently waited to start his New York campaign. Radwanska, promoted to third seed after the injury-forced withdrawal of Maria Sharapova, defeated Spanish world number 103 Maria-Teresa Torro-Flor, 6-0 7-5 while Li, the Chinese fifth seed, beat 100th-ranked Swede Sofia Arvidsson 6-2 6-2. Radwanska, who has never got beyond the fourth round in New York, was on course for a quick-fire win over Torro-Flor, her second successive Spanish opponent, when she raced through the first set in just 21 minutes, losing just seven points. But Torro-Flor, dressed in matching colours of blue and pink, made the Pole work for her win in the second set with three breaks of serve. Radwanska, however weathered the unexpected storm, going through to a third-round clash against Russia's Anastasia Pavlyuchenkova, capitalising on her rival's 38 unforced errors and 10 double faults. Li, playing in her 30th grand slam and a New York quarter-finalist in 2009, clinched her third career win over policeman's daughter Arvidsson, who has now not progressed beyond the second round in seven attempts. The Chinese star will next face either British 30th seed Laura Robson, who knocked her out of the tournament in 2012, or France's Caroline Garcia. Meanwhile, Murray begins the defence of his title almost 48 hours after second seed Rafael Nadal, viewed as the most likely contender to triumph this year, started his campaign. "I'm playing my first round match at the us open at 7pm on a wednesday...," tweeted Murray in thinly-veiled frustration at a schedule which will see even first-round matches in the mixed doubles completed before he takes the court. Having ended Britain's embarrassing grand slam hoodoo with his US Open breakthrough 12 months ago, Murray starts his first major as a defending champion against Michael Llodra, the 33-year-old Frenchman who is edging towards retirement. Also on Wednesday, women's champion Serena Williams, chasing a fifth US Open title, tackles Galina Voskoboeva of Kazakhstan. Three other former champions are also in action in the men's first round. Argentine sixth seed Juan Martin Del Potro, who defeated Roger Federer for his only major title in 2009, starts against Spain's Guillermo Garcia-Lopez while Lleyton Hewitt, the 2001 champion, faces America's Brian Baker.