Defending champion Novak Djokovic shrugged off a injury scare to win his Shanghai Masters opener on Wednesday, keeping alive the prospect of a mouthwatering quarter-final with Roger Federer, who also progressed.
Top seed Djokovic cantered through the first set against Spain's Marcel Granollers for the loss of only two games. But early in the second he pulled up in obvious discomfort and called for the ATP trainer, who applied heavy taping to his right foot and ankle.
Despite the medical treatment, the 26-year-old did not look inconvenienced as he returned to the court to seal a 6-2, 6-0 victory, hitting a total of 26 winners.
The Serb, newly dethroned from the number one ranking by Rafael Nadal, played down the incident afterwards.
"It was just an awkward movement. I was in an off-balance position. I was running and I made a quick movement that caused a sharp pain at that instant moment," he said.
"But after the match we determined that it's nothing serious, so it's all fine."
Federer, who has slipped to seventh in the world rankings and faces a battle to qualify for next month's World Tour Finals in London, won 6-4, 6-3 against Italian Andreas Seppi, after a testing start.
The Swiss great, playing his first match since a disappointing US Open, lost his serve early but broke back immediately against the world number 22, repeating the feat to take the opening set. A single break in the second was enough to seal the match.
Earlier, German world number 23 Philipp Kohlschreiber rattled a feverish Del Potro, striking 50 winners and 22 aces in a brave display of attacking tennis that had the Argentine searching for answers before he dug deep to win 3-6, 6-3, 7-6 (7/4).
Kohlschreiber won the opening set but sixth seed Del Potro, fresh from winning his third title of the year at the Japan Open, levelled the second set courtesy of a single break and kept his nerve to win a third set tie-break.
Del Potro, 25, said afterwards that he felt feverish, admitting he was lucky his opponent made errors at key moments in the tie-break.
"Last night I couldn't sleep really well," said the Argentine. "This morning I took ibuprofen, a couple of pills, trying to help me feeling better. But I'm not 100 percent yet."
"I think my serve helped me a lot to keep playing for the three sets because I made many aces," he added. "With my serve I didn't run too much. I was lucky in the tie-break because he made a few mistakes with his backhand. I won a really tough match."
Fourth seed Tomas Berdych of the Czech Republic beat Spain's Feliciano Lopez 7-6 (7/5), 6-2, and seventh seed Jo-Wilfried Tsonga eased past Spain's Pablo Andujar 6-3, 6-2.
Veteran Tommy Haas put out fellow German Daniel Brands but America's top player John Isner lost in straight sets to Argentina's Carlos Berlocq. There were also wins for seeded players Stanislas Wawrinka and Kei Nishikori.
Spain's Tommy Robredo retired from his match against Italy's Fabio Fognini with a wrist injury when trailing by a set.
Djokovic, Nadal and David Ferrer have already qualified for the end-of-season showpiece in London. Britain's Andy Murray, a beaten finalist at last year's Shanghai Masters, has withdrawn from the tournament as he recovers from back surgery.
Drenching rains earlier in the week as a result of Typhoon Fitow forced matches indoors in Shanghai, but the wet weather relented on Wednesday, allowing tournament chiefs to open the roof of the Stadium Court.