CHARLESTON, S.C. (AP) Venus Williams had not played much winning tennis since capturing her 49th WTA title in February.

She was more than ready to show off her game at the Volvo Car Open on Wednesday.

The third-seeded Williams used her powerhouse serves and crisp groundstrokes for a 6-4, 6-2 victory over fellow American Alison Riske. Williams advanced on a day when several other top seeds were upset at the year's first clay-court event.

Williams didn't care what surface she was on, the 35-year-old simply wanted to wipe away bad memories of first-match losses at Indian Wells and Miami since winning a WTA event in Taiwan two months ago.

''I just came into the tournament eager, just ready to go, especially after waiting two weeks,'' she said. ''So it's four weeks and only two matches and you're like, argh. So I usually don't have that problem.''

Williams won't have such troubles in Charleston, although several high seeds already did: No. 2 Belinda Bencic, No. 4 Lucie Safarova, No. 6 Andrea Petkovic and No. 8 Madison Keys all lost their first-matches here.

Bencic of Switzerland, ranked 10th in the world, was beaten by Russian qualifier Elena Vesnina 6-1, 6-1. Safarova, a former finalist here, fell to American wild-card entrant Louisa Chirico, 6-3, 6-3. Germany's Petkovic, the 2014 champion here, lost to Monica Puig of Puerto Rico 7-5, 6-2. Keys fell to Germany's Laura Siegemund, 6-7 (3), 6-4, 6-4. Past champion Sabine Lisicki of Germany, seeded 15th, was also ousted.

Other seeded winners along with Williams were No. 5 Sara Errani of Italy, No. 7 Sloane Stephens of the United States and 10th seeded Sam Stosur of Australia.

Williams, the seven-time Grand Slam champion, got off to a strong start at the clay-court event. She had consecutive serves of 121 mph and 119 mph to close out one game in the first set as fans in the stadium court marveled as the ball zoomed past Riske.

Williams, 35, kept up the attack throughout, winning the final four games to advance. She won the final two games without dropping a point. Riske walked to the sideline after a 102 mph ace that put Williams ahead 5-2, then the 25-year-old from Pittsburgh double-faulted to end the match.

''I think today, I was aggressive, which is important for my game, even on clay,'' Williams said. ''You still want to dictate the points.''

The top seed and defending champion, Angelique Kerber, needed a third-set tiebreaker to escape her opening match Tuesday night over Lara Arruabarrena. Kerber, the reigning Australian Open champion, returns to action at the season's first clay-court tournament on Thursday.

Eugenie Bouchard, the 2014 Wimbledon finalist, withdrew from her match with Lourdes Dominguez Lino with an injury to her lower abdomen.

Williams moved easily in her first match on clay this season and quickly erased any mistakes with her stellar play. The 2004 winner here when it was called the Family Circle Cup had her serve broken by Riske to fall behind 4-3. Williams immediately broke back then closed out the set with two more wins.

Riske broke Williams' serve to start the second set before the world's 14th-ranked player took control.

Venus and younger sister Serena have combined to win four Volvo titles in the previous 11 years. Venus Williams has never lost her opening match in Charleston in eight career appearances.

The 21-year-old Keys took a hard tumble in her loss to Siegemund while sliding for a ball in the third set and had her left wrist wrapped by a trainer.

Keys had hoped to start her clay-court season with another strong showing like last year in Charleston. She didn't lose a set on the way to the finals when Keys lost to Kerber in three sets.

This time, Siegemund's feistiness could not be matched. She continually caught Keys flat-footed on the baseline, forcing the taller American to rush up and spray returns wide. Siegemund also hung tough against Keys' powerhouse serves and forehands, sending them back often as quickly as they arrived.

''It was a very difficult match,'' Siegemund said. ''Madison played really tough when things were tight.''