World number one Justine Henin kicked off her US Open preparations with a routine 6-3, 6-1 win over Slovenia's Andreja Klepac at the Toronto Cup as Ana Ivanovic's title defence came to an abrupt end on Wednesday.
Back in action for the first time since a semi-final loss at Wimbledon, Henin showed no signs of rust as she ruthlessly dispatched the 141st-ranked Klepac in 69 minutes.
"I really needed a break after Wimbledon, mentally and physically to get fresh was really important to me," the Belgian top seed told reporters. "It's never easy to play first round.
"It took me a couple of games to find a good rhythm."
A rhythm was something Ivanovic never found, losing 6-3, 6-1 to qualifier Yan Zi of China to highlight a day of upsets.
Joining the fourth-seeded Serb at the exit door were Russian fifth and eighth seeds Anna Chakvetadze and Elena Dementieva and Czech No. 16 Lucie Safarova.
Fresh from capturing her fourth career title in Los Angeles on Sunday, Ivanovic was unable to carry the momentum to Canada, the 169th-ranked Yan disposing of the world number four in 65 minutes to record the biggest victory of her career.
Yan, who has had to qualify for all seven WTA Tour events she has played this season, took charge quickly by breaking Ivanovic at the first opportunity to go up 2-0 in the opening set.
BROKE BACK
Ivanovic, playing her first match after receiving a first- round bye, immediately broke back to level at 2-2 but Yan was undeterred, winning eight of the next nine games to take the opening set and a 4-0
"She (Ivanovic) is a top player, I think today I was very lucky," Yan told reporters. "Today I was very relaxed because she is a top player and I didn't think I could win so I just go on to the court to enjoy the match."
The day began with Italy's Francesca Schiavone ending Dementieva's title hopes with a gritty 6-7, 6-3, 6-2 comeback win, while American Meghann Shaughnessy shook off her indifferent form to surprise Safarova 3-6, 6-4, 7-5.
A trio of Frenchwomen made it through to the last 16, Wimbledon finalist and seventh seed Marion Bartoli and Virginie Razzano advancing when their opponents were forced to retire with injuries.
Chakvetadze, with hardcourt wins in Cincinnati and Stanford last month, retired in the second set with a viral illness trailing Razzano 7-6, 2-0 and Bartoli advanced when Russia's Maria Kirilenko stopped in the second set with a knee injury.
Twelfth seed Tatiana Golovin joined her French compatriots in the third round by easing past Slovakia's Dominika Cibulkova 6-4, 6-3.
Second seed Jelena Jankovic of Serbia, a four-times winner this season, contributed to a miserable day for Canadian fans by demolishing Marie-Eve Pelletier 6-0, 6-1.