French Open: Sunday 25 May to Sunday 8 June BBC TV, BBCi, Radio 5 Live and the BBC Sport website. Coverage:
Jankovic needed more than an hour to win the first set
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.
Venus has never won the French Open
"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.
"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.