Li Na of China returns the ball to Kateryna Bondarenko of Ukraine in the first round of the U.S. Open tennis tournament in New York, Tuesday, Aug. 31, 2010. Bondarenko upset eighth-seeded Li 2-6, 6-4, 6-2. [Xinhua/Shen Hong]

"It was sad to lose in the first round," Li said. "I just have to forget everything and practice again and I hope I come back again soon."

Li won the third career WTA singles title at Birmingham in June and impressed with her success at Melbourne in January.

"I had a good beginning of the year," Li said. "But in tennis, you never know. You have to play against your opponent, yourself, everything."

Bondarenko, ranked 59th, was a US Open quarter-finalist last year for her best career Grand Slam showing. She advanced to a seond-round match against either Slovakia's Dominika Cibulkova or Swiss Stephanie Voegele.

Li, who won her only prior meeting with Bondarenko last year in Tokyo, saved four break points in the first game on the way to holding serve and rolled through the opening set.

Bondarenko broke Li in the third game of the second set but Li broke back immediately and they battled to 4-4 before Bondarenko made her move.

Li, 28, sent a forehand beyond the baseline on the Ukranian's first break point of the ninth game and Bondarenko, 24, held to take the set, denying two break-point chances for Li with service winners before forcing a third set.

Bondarenko broke Li to open the third set and again in the fifth game when Li sent a forehand wide to seize a 4-1 edge.

Bondarenko hit an ace and a service winner to deny Li on break points in the sixth game and held for a 5-1 lead, then held again to claim the match after one hour and 43 minutes.