Victoria Azarenka battled back from a set and 4-0 down to defeat Italy's Alberta Brianti and avoid becoming the first top seed in history to be knocked out in the French Open first round.
World No.1 Azarenka staged a thrilling recovery to defeat world No.105 Brianti 6-7 (6-8) 6-4 6-2 and will next face German qualifier Dinah Pfizenmaier.
But for much of her rollercoaster battle with the 32-year-old Brianti, who had never won a match in four previous main draw appearances at Roland Garros, the Belarussian struggled.
Brianti was on the verge of a 5-0 lead in the second set when the Australian Open champion sent down a second serve ace to stay in contention.
That proved to be the significant moment in the tie as Azarenka, who finished with 60 unforced errors, reeled off 12 of the last 14 games.
"I started well but my game just collapsed," admitted 22-year-old Azarenka, twice a quarter-finalist in Paris.
"I tried to stay concentrated but I don't know how I got out of it.
"I was lucky.
"I made 60 unforced errors and that says it all. Bad days happen, I made way more mistakes than usual. I still got through and to commit so many errors and still win, that's a good statistic."
She also admitted that victory was down to a change in mindset on her part.
"Before maybe I would have given up and thought about what was the time of the next flight back to Minsk, but I didn't want to leave too soon. She pushed me all the way. I had to dig deep."
Defending champion Li Na of China advanced to the second round with a 6-2 6-1 win over Romania's Sorana Cirstea, a quarter-finalist in 2009.
"I'll just try my best," Li said, when asked to rate her chances of a successful defence. "It's tough for me to stay at the same level all the time."
Li will face either Barbora Zahlavova Strycova of the Czech Republic or France's Stephanie Foretz Gacon for a place in the last 32.
Polish third seed Agnieszka Radwanska took just 49 minutes to wrap up a 6-1 6-0 win over Serbia's Bojana Jovanovksi and will face Venus Williams for a place in the last 32.
French eighth seed Marion Bartoli also went through, beating Czech qualifier Karolina Plizkova 6-3 6-3.
Vera Zvonareva, the 11th seed, withdrew suffering from a right shoulder injury while German 12th seed Sabine Lisicki slumped to a 6-4 6-3 defeat to America's Bethanie Mattek-Sands.
The United States already have 10 women in the second round, their best performance since 2003.