French Open favourite Justine Henin-Hardenne and second seed Maria Sharapova gave unconvincing displays in the first round on Tuesday.
After racing through the first set against Conchita Martinez, Henin-Hardenne slumped in the second and struggled to a 6-0 4-6 6-4 win.
Sharapova trailed 3-1 in the final set against Evgenia Linetskaya before coming through 6-7 6-2 6-4.
Ameile Mauresmo had an easier time, thrashing Evie Dominikovic 6-2 6-1.
On a good day for Russia, US Open champion Svetlana Kuznetsova also went through with few problems, beating Mathilde Johansson of France 6-1 6-1.
Compatriot Anna Chakvetadze beat 26th seed Paola Suarez 7-5 1-6 6-0, and seventh seed Nadia Petrova saw off Mashona Washington 6-4 6-2.
Henin-Hardenne came into the tournament on the back of three successive titles and 17 straight wins, and looked set to overwhelm former Wimbledon champion Martinez.
The first set took just 19 minutes but, after a 20-minute opening game in the second set, two double faults and a missed smash from Henin-Hardenne at 4-5 saw Martinez level.
Henin-Hardenne had lost her rhythm and in a scrappy third had match points at 5-1, before finally securing a second-round clash with Virginia Ruano Pascual or Anastasiya Yakimova four games later.
"It was a very strange match," said Henin-Hardenne. "I played extremely well in the first set, probably the best set I've ever played.
"But then I thought everything was going too well and lost my concentration. Conchita also started playing a lot better.
"She's got a lot of experience so she knew she had to change things and she did."
Sharapova was even closer to defeat against Linetskaya, but insisted she enjoyed the experience.
"This is the sort of match that you live for," said Sharapova.
"When you're a break down in the third, you're just begging for mercy, and then to pull it back.
"It definitely wasn't the best match I've played but when you don't play well and you get through that also means a lot."