PARIS -- Reigning US Open champion Sloane Stephens needed less than an hour to move into the second round of the French Open on Sunday, but Venus Williams and defending champion Jelena Ostapenko are out on the opening day.
Williams, the 2002 runner-up and ninth seed, lost 6-4, 7-5 to Wang Qiang of China in the first round on Court Suzanne Lenglen.
Wang avenged her loss to Williams in the first round at Roland Garros last year. The 85th-ranked player was also beaten by Williams at Wimbledon a few weeks later and had never beaten Williams before Sunday.
It's the fourth time Williams, 37, exits the French Open in the first round in 21 appearances.
She also lost in the first round at the Australian Open in January.
The 10th-seeded Stephens advanced at Roland Garros with a 6-2, 6-0 victory over Arantxa Rus of the Netherlands. It was Stephens' first win at a Grand Slam tournament since claiming her first major title in New York last September.
"I tried to do way more than I should have after the US Open, and I should have just shut it down," Stephens said when asked about her poor recent results. "My heart was there but my body wasn't. So when the two things aren't connected, it's never a good thing."
The American, who lost in the first round at the Australian Open in January, hit 17 winners and spent just 49 minutes on court on Day 1 in Paris. Rus was in the first round as a "lucky loser."
The fifth-seeded Ostapenko, who upset Simona Halep in last year's final, lost 7-5, 6-3 against Kateryna Kozlova of Ukraine on Court Philippe Chatrier.
"Just amazing feeling," said Kozlova after posting her first win over a top-30 player.
Ostapenko became only the sixth defending women's champion to lose in the opening round of her title defense at a major tournament.
On a sunny and warm day, Stephens was joined in the second round by fourth-seeded Elina Svitolina, who defeated Ajla Tomljanovic 7-5, 6-3 after recovering from a 5-1 deficit in the opening set.
France's Alize Cornet is also through to the second round, beating 2012 runner-up Sara Errani of Italy 2-6, 6-2, 6-3.
Cornet, seeded 32nd, is playing her 14th Roland Garros. She was cleared of a doping charge by an independent tribunal earlier this month.
Another seeded player, No. 22 Johanna Konta of Britain, was handed an early exit on the red clay of the French Open, beaten 6-4, 6-3 by Yulia Putintseva of Kazakhstan.
The British No. 1 has never won a match in Paris in four appearances in the main draw.
Two matches have been left unfinished at the French Open as play was suspended Sunday night because of darkness.
Qualifier Alexandra Dulgheru of Romania and American Christina McHale were level at one set apiece on Court 7, while Pauline Parmentier led Chloe Paquet 3-6, 7-6 (4), 3-1 on Court Suzanne Lenglen in an all-French matchup.