TORONTO (Reuters) - World number one and holder Dinara Safina made an early exit from the Toronto Cup on Wednesday, shocked 3-6 6-2 6-4 in the second round by 39th ranked Frenchwoman Aravane Rezai.
There were no such slip ups from world number two Serena Williams, however, as the Wimbledon and Australia Open champion rolled to a 6-3 6-2 win over Kazakh qualifier Yaroslava Shvedova.
The two results set up the possibility of a spicy subplot to the U.S. Open, where the debate over who should be women's number one could be settled on court.
While Williams cannot overtake Safina with a victory in Toronto, a win would allow the American to slice a huge chunk off Safina's 1,004 point advantage, putting the Russian well within striking distance at Flushing Meadow.
Without a grand slam title on her resume, Safina has been forced to repeatedly defend her number one status while Willliams, who currently holds three grand slam titles, has been dismissive of the rankings system.
"I don't follow the rankings anymore, been there done that," said Williams, who held the number one spot for 11 weeks earlier this year. "My motivation is to just go out there and play my best whether I'm number one or number 100."
Safina, eight times a finalist this season including last week in Cincinnati, could not find her feet on the Canadian hardcourt and contributed to her own demise by serving up 17 double faults.
The victory was the first win in three visits to Canada for Rezai and earned her a small measure of revenge for the 6-1 6-0 hammering she suffered at the hands of the Russian in the French Open fourth round earlier this year.
"Disaster," Safina, close to tears, told reporters. "It's not my serve, it's just my brain. I know exactly what I have to do but I am not using my brain.
"I just didn't take control of my head. I lost my temper. I had to slow down and I couldn't do the right things. I just went more and more crazy."
With third seed Venus Williams already out, the top half of the draw has opened up for two former number ones on the comeback trail, Maria Sharapova and Kim Clijsters.
Sharapova, working her way back to top form after nine months recovering from shoulder surgery, also served up 17 double faults but survived to book her place in the last 16 with a 6-3 7-6 win over Austria's Sybille Bammer.
"I'm having a competition with myself to see how many errors and double faults I can make and still win a match in two sets," said Sharapova. "The more I was out there today the worse I was playing."
Clijsters, playing just her second event since coming out of a two-year retirement, battled to a 7-5 4-6 6-1 win over ninth seeded Victoria Azarenka of Belarus.
"I think I fought very well and I felt like I was playing at the level I want to play," said the Belgian. "I always try to raise my level to the opponent I play."
Fifth seed Jelena Jankovic, another former number one, also advanced with a 7-5 6-4 win over Swiss Patty Schnyder while her 11th seeded fellow Serbian Ana Ivanovic fell to Czech qualifier Lucie Safarova 3-6 7-5 6-3.
Editing by Nick Mulvenney