(CNN) -- Venus Williams has crashed out of the Rodgers Cup in Toronto after a shock 1-6 7-5 6-4 second round defeat by qualifier Kateryna Bondarenko.
Venus Williams won the opening set before crashing out of the Rodgers Cup to Kateryna Bondarenko.
It all seemed to be going to plan for third seed Williams, who had a bye in the first round, when she made light work of the opening set.
But Bondarenko broke in the first game of the second set and, although Williams broke straight back, the Ukrainian went on to level the match.
Bondarenko broke the five-time Wimbledon champion's serve again in the ninth game of the third set and held on to beat the elder Williams sister for the first time in three meetings.
"I was definitely expecting to play well and to go very far in the tournament," Williams told reporters. "It's very disappointing."
There was also a shock in the day's other second round match when in-form Samantha Stosur defeated Russian sixth seed Svetlana Kuznetsova 6-4 6-3.
Australian Stosur will next face either France's Virginie Razzano or another in-form player, Italy's Flavia Pennetta, in the second round.
Meanwhile, in the first round, Ana Ivanovic fought back after losing the opening set to see off qualifier Magdalena Rybarikova 2-6 6-3 6-2 in just under two hours.
The number 11 seed got off to a poor start but eventually got into her stride to secure herself a second-round meeting with Lucie Safarova, who beat Kaia Kanepi in straight sets 6-4 7-6.
Number 16 seed and last year's runner-up Dominika Cibulkova is safely through after she dispatched Sara Errani 6-4 6-2.
Elena Vesnina's service struggles contributed to her crashing out of the tournament 6-3 6-2 to China's Jie Zheng. The Russian hit eight double faults and only won 33 per cent of points on her serve.
Elsewhere in the first round, Alla Kudryavtseva beat Julie Coin 2-6 6-1 7-6 and Shahar Peer saw off Monica Niculescu 6-4 4-6 7-6.