Kateryna Bondarenko of Ukraine upset third-ranked Venus Williams 1-6, 7-5, 6-4 in the second round of a two million-dollar WTA hardcourt tournament here on Tuesday.
Williams, who enjoyed a first-round bye, roared to a quick victory in the opening set but by the finish had fallen to 0-3 all-time in the Canadian WTA event, the final major tuneup for many players ahead of the US Open.
"I was definitely expecting to play well and to go very far in the tournament," Williams said. "It's disappointing."
Williams was not the only seed sent packing.
Australian Samantha Stosur defeated Russian sixth seed Svetlana Kuznetsova 6-4, 6-3. The Aussie will next face either France's Virginie Razzano or Italy's Flavia Pennetta.
Williams saw a silver lining in the loss, knowing she had almost two weeks to rest before the year's final Grand Slam event starts at Flushing Meadows.
"I have to take it as a positive," Williams said. "Now it'll give me a chance to rest. It has been a really busy summer for me."
Bondarenko, ranked 64th, will face either Hungary's Agnes Szavay or Poland's Agnieska Radwanska in the third round.
"It's big because it was against Venus," Bondarenko said. "I was playing really good. The first set, I didn't know what to do with her power. The rest of the time, I just tried to keep the ball in play."
Serbian standout Ana Ivanovic advanced to the second round by rallying to defeat Slovakia's Magdalena Rybarikova 2-6, 6-3, 6-2.
Ivanovic, the 21-year-old world number 11 still seeking her first WTA title of the year, made seven double faults but outlasted her 47th-ranked rival.
"My movement, my shots, everything was working well, but I was trying to play a little too safe," Ivanovic said. "She's a good player and she was playing really aggressive and dominant."
Ivanovic's next opponent will be Czech Lucie Safarova, who defeated Estonia's Kaia Kanepi 6-4, 7-6 (7/3).
China's Zheng Jie ousted Russia's Elena Vesnina 6-3, 6-2, and could face Kim Cljisters, making a comeback after taking a two-year break to start a family, in a second-round match.
Israel's Shahar Peer took more than two and half hours but finally advanced past Romania's Monica Niculescu 6-4, 4-6, 7-6 (7/4).