Third seed Jelena Jankovic hit back after a sluggish start to beat Romanian debutant Monica Niculescu and reach the second round of the French Open.
The Serb, a semi-finalist at Roland Garros last year, edged a scrappy first set featuring six breaks of serve before prevailing 7-6 (7-3) 6-2.
"I had a good start and then she played some great shots, some fine drop shots. I got confused," said Jankovic, 23.
Venus Williams struggled to a 6-3 4-6 6-2 win over Israel's Tzipora Obziler.
The American, the eighth seed, made 39 unforced errors and dropped serve four times as she ground out an unconvincing win over 35-year-old Obziler, the oldest woman in the field.
"She played very well, she was determined but I finally figured it out," said Williams, who will now meet Tunisia's Selima Sfar.
Williams is a possible quarter-final opponent for Jankovic, who is one of the favourites for the title following defending champion Justine Henin's retirement.
The 23-year-old, winner of the Italian Open, faces Italian Tathiana Garbin or Marina Erakovic in the second round.
"I don't see myself as the favourite," insisted Jankovic.
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"I am the number three in the world. There are others who are favourites but I feel I have made improvements.
"I am more mature. I have played in three Grand Slam semi-finals and lost to the eventual winner. Justine was the one against whom I always had the most trouble, so I have a better chance now."
Patty Schnyder - the 10th seed from Switzerland - beat Russia's Ekaterina Bychkova 6-3 6-4.
Agnes Szavay, the 12th seed from Hungary, was taken to three sets before reaching the second round with a 6-1 4-6 6-4 win over Ayumi Morita of Japan.
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