Venus Williams loses in opening round of Rio 2016 Olympics

Venus Williams' hopes of winning another Olympic gold medal now rest in the women's doubles after the veteran tennis star lost her opening singles match at the Rio Games on Saturday.

The American has had a resurgence this year, reaching the semis at Wimbledon and a WTA Tour final in Stanford, but lost in three sets to 62nd-ranked Kirsten Flipkens.

The Belgian won 4-6 6-3 7-6 (7-5) in a three-hour thriller to set up a second-round clash with Czech Lucie Safarova, who also came from behind to beat Italy's Karin Knapp 4-6 6-1 6-1.

"I've never played the Olympics before so it was already a dream coming true for me to come here," Flipkens said.

"I qualified for it, I worked a year for this, not to get medal but just to qualify and come here, but then to beat Venus Williams, one of the biggest champions in our history, on center court, gives me goose bumps all over the place."

The 36-year-old Williams won singles gold at Sydney 2000, but her three other Olympic titles are in the doubles with younger sister Serena. They will defend their crown from London 2012 in Brazil, starting with Sunday's match against Safarova and Barbora Strycova.

World No. 1 Serena begins her singles title defense Sunday against Australia's Daria Gavrilova, while men's champion Andy Murray starts his campaign against Serbia's Viktor Troicki.

Troicki's compatriot Ana Ivanovic also crashed out in the opening round, squandering a lead as she lost 2-6 6-1 6-2 to Spanish ninth seed Carla Suarez Navarro.

Serbia did have some good news, as men's No. 1 Novak Djokovic won his opening doubles match with Nenad Zimonjic, beating Croatian rivals Marin Cilic and Marin Draganja.

"I didn't play doubles in last two years, maybe four matches, so I'm not as comfortable as on the singles court, but I must say we played on a very high level," Djokovic said after a straight-sets victory.

Polish fourth seed Agnieszka Radwanska was another high-profile player to exit, losing 6-4 7-5 to China's world No. 64 Zheng Saisai.

U.S. seventh seed Madison Keys went through to round two but Sloane Stephens lost her North American battle with Canada's Eugenie Bouchard. There are only three Americans left in the singles after Jack Sock, Brian Baker, Denis Kudla also lost.

In the men's draw, French second seed Jo-Wilfried Tsonga won his opening match, as did Japan's No. 4 Kei Nishikori and No. 9 Cilic.

Both competitions have been hit by withdrawals, with Swiss duo Roger Federer and Stan Wawrinka injured while the likes of Tomas Berdych, Milos Raonic and Simona Halep cited heatlh fears due to the Zika virus.