(CNN) -- U.S. number one Mardy Fish is out of the Shanghai Masters after slipping to a 4-6 6-1 6-4 second round defeat to Australia's Bernard Tomic.
Fish, seeded fifth for the Chinese event, had beaten his 18-year-old opponent at the Japan Open just four days ago, but he was less successful Tuesday as his hopes of a seventh Tour title came to a premature end.
"I can't expect much more from myself," world No. 49 Tomic told the Tour's official website. "I've had a good six months.
"I'm playing well here. The surface, conditions suit me. I think it's been a good run. I've got to play well now in the third round. I think I've got a lot more to improve in the next few years."
Tomic has enjoyed a breakthrough year in 2011, reaching the quarterfinal finals of Wimbledon in July.
Fish's compatriot Andy Roddick was in better form, the 2003 U.S. Open winner recording a 7-6 (7-3) 7-5 success over Bulgarian Grigor Dimitrov to reach the third round of the tournament for the first time in his career.
"I felt like I was returning pretty well and hitting my forehand pretty well," said Roddick, 29. "Then all of a sudden, I'm not putting a first serve in the court. I felt like I was getting it backwards a little bit.
"[I] got through it, though. I do that pretty well, get through matches when everything doesn't go perfectly. There's no such thing as a bad win. I'll keep going in this tournament hopefully."
Next up for Roddick is Spanish seventh seed Nicolas Almagro, who defeated his fellow countryman Tommy Robredo 7-5 6-3.
Frenchman Gilles Simon is also into the third round courtesy of a straight-forward 6-1 6-1 triumph over Albert Montanes in just 58 minutes.
Donald Young was another American to taste defeat, losing 6-7 (5-7) 7-6 (7-2) 6-2 to Switzerland's Stanislas Wawrinka, while 2002 Wimbledon finalist David Nalbandian was eliminated by Germany's Florian Mayer.
Elsewhere, U.S. Open champion Samantha Stosur avoided embarrassment as she battled to beat Thai qualifier Noppawan Lertcheewakarn 6-3 3-6 7-5 in the opening round of the Japan Women's Open.
The top seed's second round opponent will be Japan's Misaki Doi, who got the better of American Coco Vandeweghe 6-4 6-4.
French second seed Marion Bartoli is also safely through courtesy of a 6-2 6-2 defeat of Hungary's Melinda Czink.
German Angelique Kerber cruised through her first round match as the third seed notched a 6-2 6-1 victory over Japanese wildcard Kurumi Nara.