Djokovic canters as Del Potro plods in Shanghai

The Serb, who lost his world number one ranking to Rafa Nadal on Monday, needed some treatment on his right foot during the second set but it did not stop him from breaking his opponent three times to win at a canter.

(Reuters)

Sixth seed Juan Martin del Potro overcame a slow start to beat German Philipp Kohlschreiber 3-6 6-3 7-6(4).

Kohlschreiber, ranked number 23 in the world, served 22 aces and hit 50 winners against a sluggish del Potro. But the Argentine, who said he had been feeling ill, fought back to get an early break in the second set and get a grip on the match.

"It was really tough for me," del Potro, who later withdrew from doubles, told reporters. "I couldn't run a lot. I think my serve helped me a lot to keep playing for the three sets because I made many aces.

"With my serve I didn't run too much. I was lucky in the tie-break because he made a few mistakes. I won a really tough match."

France's Jo-Wilfried Tsonga had a much easier start to his campaign as he brushed aside Pablo Andujar 6-3 6-2 in 65 minutes.

Tomas Berdych of Czech Republic, currently sixth in the race for next month's ATP World finale in London, also took a positive step towards sealing his berth by defeating Spain's Feliciano Lopez 7-6(5) 6-2.

(Writing by Sudipto Ganguly)