Adelaide, Australia: Lleyton Hewitt, playing singles for the first time since a Davis Cup loss three months ago, beat Serbia's Janko Tipsarevic at the Adelaide International on Tuesday after Tipsarevic retired late with a thigh injury.The former world No. 1 Australian was leading the round-robin match 6-1, 4-2 when Tipsarevic decided he could not continue.Hewitt, whose last singles match was a five-set loss to Argentina's Jose Acasuso in the Davis Cup semifinals in September, had little trouble after Tipsarevic made a number of early unforced errors.Down 2-0 in the second set, Tipsarevic requested an injury timeout and won two more service games before deciding not to continue. Hewitt said he was dubious about the extent of Tipsarevic's injury."After the injury break, I still felt like I was moving him around the court and coming up with some decent shots," said Hewitt. "There was one backhand he rifled up the line ... if he had that bad a groin, I don't know how he would have pulled that off."I had my game plan. I wanted to get away with a straight-sets win and I was able to do that."Hewitt's next match will be on Thursday against Russia's Igor Kunitsyn.Earlier, Novak Djokovic of Serbia and France's Richard Gasquet showed little signs of rustiness during their opening matches of the 2007 season.Djokovic, 19, defeated Czech Jan Hajek 6-0, 6-1 in 57 minutes."It is a great thing to finish the match in less than one hour in these conditions because it's really hot out there and it's getting hotter," said Djokovic."I played a really, really good first match today with a great performance and the guy didn't really play his best for sure, but I didn't allow him to play his game."Gasquet, 20, needed 49 minutes to beat Germany's Florian Mayer."It was a good match, it was difficult for me because it was the first of the year," said Gasquet.The tournament lost its first seeded player when No. 5 seed Dominik Hrbaty lost to American Paul Goldstein 6-2 7-6 (4). Goldstein will now play Australian Alun Jones on Wednesday for a place in the quarterfinals.Third-seeded Radek Stepanek will need to defeat Russian Evgeny Korolev in his next round-robin match to have a chance of progressing to the final eight after losing to American Vince Spadea 6-4, 6-4 on Tuesday.The 32-player Adelaide tournament is the first to try the ATP Tour's new round-robin format in 2007.A dozen other tournaments are expected to experiment with the format during the season.