Nadal through in Shanghai, Del Potro retires

Top seed Rafa Nadal marched into the last 16 of the Shanghai Masters with a thoroughly entertaining 6-2, 6-7, 6-4 victory over American James Blake on Wednesday.

US Open champion Juan Martin Del Potro, however, joined the growing casualty list at the $3.24-million tournament, retiring because of a wrist injury while 7-5, 2-1 down to Austrian Jurgen Melzer.

World number two Nadal beat Blake in three sets on his way to the semi-finals in Beijing last week and on Wednesday needed more than two hours to get past the man he rates as having one of the best returns in the game.

After Nadal raced away with the first set, the pair contested two absorbing sets littered with high-quality winners before Nadal, with Blake serving to take the match into a decisive tiebreak, unleashed a sizzling forehand to clinch victory.

The Spaniard has not reached a final since the Madrid Masters in May and will continue his comeback from knee and abdominal injuries against compatriot Tommy Robredo on Thursday.

Third seed Del Potro followed Andy Roddick in departing early through injury after the American fourth seed departed with a knee problem on Tuesday.

"I had this injury in Miami this year and I don't want to risk for the end of the season," said the 21-year-old Argentine, who lost his first match since his Flushing Meadow triumph to world number 189 Edouard Roger-Vasselin in Tokyo last week.

"I'm a little sorry. It's a big tournament here in Shanghai, very important for me, but if I want to have a good finish this season, I have to recover."

With world number one Roger Federer and number three Andy Murray skipping the tournament because of fatigue and a wrist injury respectively, Del Potro's departure is certain to intensify the debate over the length of the men's season.

"It's difficult to play 11 months at a high level but we know they are working on that, so we hope that there will be a good change for the future," said the world number five.

Fifth seed Jo-Wilfried Tsonga of France took exactly an hour to dismiss Chinese wild card Zeng Shaoxuan 6-3 6-3 and set up a third-round clash with Swedish ninth seed Robin Soderling, who beat Spain's Nicolas Almagro 6-4, 7-5.

Ivan Ljubicic proved it was possible to play at the top level after 30, despite the gruelling schedule, by upsetting Spanish seventh seed Fernando Verdasco 6-4, 7-6.

The Croatian will meet Gael Monfils in the last 16 after the French 11th seed rallied from a break down in the third set to beat Australia's former world number one Lleyton Hewitt 4-6, 6-4, 6-2.