Sharapova of Russia defeated Marta Domachowska of Poland 7-5, 5-7, 6-2 in a match that took nearly three hours. She will have an MRI on Thursday.
Top-seeded Ana Ivanovic, playing with a swollen thumb, advanced to the third round with a 6-3, 4-6, 6-3 win over Petra Kvitova.
Trailing 3-4 in the second set, Sharapova had the trainer come out to look at her right shoulder, an injury that might have contributed to her committing 17 double faults in the match. Though she eventually lost the second set, Sharapova won the first four games of the final set to lock up the match.
"It's obviously unfortunate,'' Sharapova said. "You know, you try to do every little possible thing you can. But at the end of the day when you go on court and you're thinking about aggravating things, you're thinking about an injury, it's not really the way to play.''
Sharapova said she considered not coming out for the third set, and she will have tests on the shoulder that's been bothering her since March when she aggravated it at Indian Wells.
She said her presence at the upcoming Olympics and the U.S. Open, which begins in late August, will depend largely on the results of the tests.
"At the end of the day, it's tough to go on court and not be close to even 50 percent,'' Sharapova said. "I'm too good of a player to go out there and try to fight through something that I think can eventually become something serious.''
Third-seeded Maria Sharapova also advanced despite an injury, beating Poland's Marta Domachowska 7-5, 5-7, 6-2. Sharapova called for the trainer trailing 3-4 in the second set to look at her right shoulder, an injury that might have contributed to her committing 17 double faults in the match.
Though she eventually lost the second set, Sharapova of Russia won the first four games of the final set to lock up the match.
Ivanovic, who hurt her right thumb while practicing 10 days ago, refused to use the injury as an excuse for her performance in her first match since Wimbledon.
In other matches, Second-seeded Jelena Jankovic of Serbia beat Aleksandra Wozniak of nearby Blainville, Quebec, 6-0, 6-4.
No. 7 seed Dinara Safina of Russia and ninth-seeded Patty Schnyder of Switzerland each advanced to the third round in straight sets.
Safina easily dispatched fellow Russian Anastasia Rodionova 6-2, 6-4. Schnyder came back from a 2-5 hole in the second set to beat Monica Niculescu 6-1, 7-5.
Sixth-seeded Russian Anna Chakvetadze of Russia beat Jill Craybas of the United States 6-2, 7-5.
Two seeds lost Wednesday. No. 13 seed Maria Kirilenko fell to local favorite Stephanie Dubois of Laval, Quebec, 6-2, 2-6, 7-6 (4), and 15th-seeded Flavia Pennetta of Italy lost 6-3, 0-6, 6-3 Michelle Larcher de Brito, a 15-year-old qualifier from Portugal.
IMMELMAN WITHDRAWS DUE TO ILLNESS
Sugiyama, Kuznetsova advance in Toronto
JIMENEZ WITHDRAWS FROM WALES OPEN
Sharapova scoots into 4th round
