Williams looked in trouble after losing the first set
27 May-10 June
TV: Coverage on BBCi throughout tournament, singles finals on BBC One and Two
Radio: Commentary on Five Live Sports Extra, 4-6 June; commentary on singles finals on Five Live
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Serena Williams recovered from an awful start to her French Open campaign to beat Bulgaria's Tsvetana Pironkova.
The Australian Open champion made 26 errors in the first set and 19-year-old Pironkova emerged from a six-hour rain delay to clinch it.
But Williams suddenly found her form and reeled off nine games in a row before triumphing 5-7 6-1 6-1.
Williams is in the same quarter of the draw as Justine Henin, a 6-4 6-3 winner over Russian Elena Vesnina on day one.
"The conditions were difficult," Williams said. "The rain really slows the court down.
"I was already coming back when there was the break and there's no way I wouldn't have gone to at least three sets.
"I'm a fighter. I've never lost in the first round of a Grand Slam and I didn't want that to change.
"I was also feeling that if I went down, there was a 99.9% chance she would lose in the next round.
"That helped me keep fighting. I couldn't lose on the Sunday, no way."
Henin, the defending champion, meets Austria's Tamira Paszek in the next round while Williams awaits the winner of a first-round match between France's Virginie Razzano and Milagros Sequera of Venezuela.
Paszek thrashed Japan's Aiko Nakamura 6-4 6-0 while the only other women's match to be completed on day one was tenth seed Dinara Safina's 7-5 6-4 win over Ukraine's Yuliana Fedak.