CARSON, Calif. -- Mary Pierce's comeback didn't go well Monday night when she lost to Tamarine Tanasugarn, 7-6 (2), 6-3, in the opening round of the JPMorgan Chase Open.

Pierce, plagued by injuries in recent years, has been trying to regain the form that carried her to two Grand Slam titles and a career-high No. 3 in the rankings. She seemed to have been making progress, too, having reached the fourth round at Wimbledon and the third round of last week's Acura Classic at Carlsbad.

Monday night, however, Pierce said she felt a pain in her back late in the prematch warmup. Trailing 3-0 in the second set, she took an injury timeout after feeling a sharp pain in her left side. She said afterward she wasn't sure if the injury was in her back or her abdomen.

"The thing that concerned me most was that it's in the same spot where I strained my abdomen pretty bad in Melbourne two years ago," Pierce explained. "I could feel it in my back when I was serving. What concerned me was that it might be something that could maybe be more serious if I don't take care of it.

She planned to consult the WTA Tour trainer before deciding whether to play her scheduled doubles match Tuesday.

In the final match of the night, Arantxa Parra of Spain defeated Angela Haynes 6-1, 6-4, taking the final five games of the match.

Earlier Monday, Maria Sharapova posted a 6-3, 6-1 victory over Katarina Srebotnik. It was the first tour match for the 16-year-old Sharapova since her three-set loss to Svetlana Kuznetsova in the fourth round at Wimbledon.

Restricted in the number of tournaments she can play because of the tour's age-eligibility rule, Sharapova spent the last few weeks playing World Team Tennis. Ranked 56th in the world, Sharapova said the three-week WTT season was beneficial because she was able to play singles and doubles.

But she was happy to rejoin the tour for her eighth event of the year. Her record is 8-7 overall, but she has won eight of her last 10 matches.

"It was pretty good, actually," she said. "I played pretty good. I haven't really played in a big match since Wimbledon so that was pretty exciting for me, and I haven't played on hard (courts) in a while. I think I could have played a little bit better, but it was solid."

Sharapova, a 6-footer who is still growing, took control against Srebotnik by winning the final three games of the opening set and the first three of the second.

Sharapova's Russian countrywoman, Elena Likhovtseva, also advanced to the second round with a 6-1, 6-1 win over Akiki Morigami of Japan.

In other first-round matches, Rita Grande of Italy beat Janette Husarova of Slovakia 6-3, 5-7, 6-4; Emilie Loit of France eliminated Yoon Jeong Cho of Korea 6-3, 6-2; Saori Obata of Japan rallied to defeat Virginie Razzano of France 2-6, 6-2, 6-3; and Shinobu Asagoe of Japan topped Els Callens of Belgium 6-3, 3-6, 6-3.

American qualifier Tara Snyder also advanced when Marion Bartoli of France retired in the second set with a strained right elbow. Snyder was leading 6-3, 4-2 when the match was called.