Maria Sharapova, of Russia, grimaces as she serves to Poland's Marta Domachowska during second-round action at the Rogers Cup Wednesday night. (Jacques Boissinot/Canadian Press)

Maria Sharapova won her opening match at the Rogers Cup Wednesday night but then bid adieu to the Montreal fans when she decided to pull out of the tournament.

Citing a right shoulder injury, the world No. 3 made the decision shortly after posting a 7-5, 5-7, 6-2 victory over Poland's Marta Domachowska in an evening match that took nearly three hours.

The Russian star, who has been bothered by the injury since March, will visit a doctor Thursday for an MRI. She said her participation at the 2008 Beijing Olympics and the U.S. Open next month will depend largely on the results from Thursday's tests.

"At the end of the day, it's tough to go on court and not be close to even 50 per cent," 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."

Sharapova had the trainer come out as she was trailing 3-4 in the second set to look at her right shoulder, which may explain why she committed 17 double faults in the match.

"I was not even sure if I was going to continue in the beginning of the third set because it was getting worse as the match went on," Sharapova said. "It's tough to fly all the way to Montreal and play two sets and say, `I'm done.' Maybe that's the right thing to do. But I have too many fans out there watching me that support me on a daily basis to kind of say, I'm going to head home. At least I finished the match."

Dubois the lone Canadian

Earlier in the day, Stephanie Dubois of Laval, Que., upset No. 13 Maria Kirilenko of Russia 6-2, 2-6, 7-6, (4) in a fiercely contested battle that lasted just under three hours at Uniprix Stadium.

"I'm very happy I was able to keep fighting right to the end and go get the win," Dubois told the crowd after the match. "I was aggressive at the end and I'm really happy I was able to finish in style."

Dubois moves on to the third round where she will face No. 2 seed Jelena Jankovic of Serbia, who defeated the only other Canadian left in the draw, Aleksandra Wozniak, 6-0, 6-4 in the night session.

Wozniak, from Blainville, Que., came into this tournament riding a wave of momentum. She recently became the first Canadian woman to win a WTA tour event in 20 years, defeating the likes of Serena Williams, Marian Bartoli and Francesca Schiavone at the Bank of the West Classic in Stanford, Calif.

But the 20-year-old never fully recovered after being overwhelmed by Jankovic in the first set, much to the chagrin of the Montreal fans who were hoping to witness another Canadian upset.

"I had nothing to lose, but she really played a perfect match with very few errors," Wozniak said."

Dubois goes toe-to-toe with Kirilenko

Dubois put Kirilenko on the defensive quickly on her second match point, hitting a backhand volley that the Russian returned into the net.

Currently ranked 122nd as a singles player, Dubois made a critical error that almost cost her the match. With the score 4-4 in the third set, she challenged a line call instead of playing it.

The call went against her and her serve was broken, but she broke back in the next game.

She jumped ahead 4-2 at the first tiebreak rest, staying in the rallies on two points until Kirilenko made unforced errors.

Kirilenko appeared to be unsettled by the increasingly vocal Uniprix crowd, plugging her ears while walking to her chair late in the third set.

"I see it more as positive pressure," Dubois said of the support she received from the Montreal crowd. "It gives you a push having the crowd behind you."

Top seeds make debut

Wednesday was the first day of action for many of the top eight seeds, who received byes into the second round.

World No. 1 Ana Ivanovic of Serbia defeated the Czech Republic's Petra Kvitova 6-3, 4-6, 6-3.

Ivanovic was playing with a swollen right thumb, but she refused to use that as an excuse for her sluggish performance in her first match since Wimbledon.

"I went on the court and that means that I felt 100 per cent ready to play," Ivanovic said. "So, obviously it takes some time to get in a rhythm. But I went through this match. It would probably be the same even if I was feeling 100 per cent."

No. 6 Anna Chakvetadze was a 6-2, 7-5 victor over American Jill Craybas. The Russian Chakvetadze is looking for a strong finish to the summer after disappointing Grand Slam results in 2008.

Dinara Safina was a straight-sets winner over fellow Russian Anastasia Rodionova. Seeded seventh, Safina won by scores of 6-4, 6-2.

The sister of Marat Safin, she advanced to the third round and will face No. 9 Patty Schnyder of Switzerland, who defeated Monica Niculescu of Romania 6-1, 7-5.

Victoria Azarenka of Belarus also moved on to the third round. The No. 11 seed, who turns 19 on Thursday, defeated Austrian veteran Sybille Bammer 6-2, 6-2.

Tenth-seeded Marion Bartoli of France had the easiest day. Bartoli advanced when Alisa Kleybanova of Russia withdrew from the tournament because of a bad back.

In other results on Wednesday:

• No. 12 Nadia Petrova of Russia was a 6-3, 6-2 winner over Tamarine Tanasugarn of Thailand.
• Ai Sugiyama of Japan defeated Shahar Peer of Israel 6-2, 6-2.
• Tamira Paszek of Austria topped Melinda Czink of Hungary 6-4, 7-5.
• Portugal's Michelle Larcher de Brito, 15, eliminated Flavia Pennetta of Italy 6-3, 0-6, 6-3.

With files from the Canadian Press