Third seed Venus Williams's return to Canada ended in a shock 1-6, 7-5, 6-4 second-round defeat by Ukrainian qualifier Kateryna Bondarenko at the Toronto Cup on Tuesday.
Kim Clijsters' return, however, had a much happier ending as the hugely popular 2005 champion continued her comeback from a two-year absence with a business-like 6-3, 6-4 first round victory over British qualifier Elena Baltacha.
However the 64th-ranked Bondarenko refused to fold, trading breaks with the 29-year-old American in the second before finally taking control of the set with another break at 6-5 and then holding serve to level the match.
As a frustrated Williams sprayed shots all over the court Bondarenko began to find her mark, recording the only break of the third set to go 5-4 up before clinching victory.
"I guess at this tournament I've never had a lot of luck but I guess you have to make your own luck these days," Williams told reporters. "She (Bondarenko) just really started playing well and unfortunately I made too many errors.
"She kept a lot of balls in play and ran a lot of balls down. I was expecting to play well and go far in the tournament."
Williams was joined at the exit by Russian sixth seed Svetlana Kuznetsova, with the French Open champion falling 6-4, 6-3 to Australian Samantha Stosur.
Clijsters, who made a stunning return to the WTA Tour last week in Cincinnati reaching the quarter-finals, simply outclassed her 104th ranked British opponent in Toronto wrapping up the contest in a tidy 68 minutes.
"I still feel like I have a long road ahead of me to get back to where I was," the Belgian former world number one, who gave birth to her first child in February 2008, said.
"But it's a challenge and that's why I decided to come back to see if I can still make myself get up there.
"It's a big challenge but it's one I really look forward but I definitely still have a lot of work to do."
In other first-round action, ninth seed Victoria Azarenka of Belarus eased past China's Peng Shuai 6-3, 6-3 while 11th-seeded Serb Ana Ivanovic needed three sets to beat Slovakian qualifier Magdalena Rybarikova 2-6, 6-3, 6-2.
Italian 12th seed Flavia Pennetta advanced with a routine 6-3, 6-3 win over Russian Maria Kirilenko while 16th seed Dominika Cibulkova of Slovakia beat Italy's Sara Errani 6-4, 6-2.