Three-time doubles gold medalists Serena and Venus Williams lost an Olympic match as partners for the first time, stunned in the first round Sunday by the Czech Republic's Lucie Safarova and Barbora Strycova 6-3, 6-4.

The Williams sisters had been 15-0 in the Olympics, winning gold every time they had entered doubles: in 2000, 2008 and 2012.

Neither Safarova nor Strycova had won an Olympic doubles match, going a combined 0-3 with other partners. And they weren't even supposed to be playing together at the Olympics. Strycova was a late replacement for Karolina Pliskova, who withdrew from the tournament.

Indeed, Strycova and Safarova had played only one match as a team before Sunday night, losing in a Fed Cup match last year.

In singles, Serena opened defense of her Olympic title with a 6-4, 6-2 victory over Australia's Daria Gavrilova.

On the men's side, world No. 1 Novak Djokovic of Serbia was upset by Juan Martin Potro of Argentina 7-6 (4), 7-6 (2). ... Rafael Nadal, who hadn't played since withdrawing from the French Open because of an injury, rolled over Argentina's Federico Delbonis 6-2, 6-1. And defending champ Andy Murray beat Serbia's Viktor Troicki 6-3, 6-2. But Murray and his brother Jamie lost in doubles to Brazilians Thomaz Bellucci and Andre Sa 7-6 (6), 7-6 (14).

Intensive scare: Dutch cyclist Annemiek van Vleuten suffered three small fractures to her spine and was in intensive care after crashing during the women's road race.

Van Vleuten was leading on the fast, slippery downhill toward the final stretch when she tumbled onto the road. She was conscious and speaking.

Compatriot Anna van der Breggen won gold.

Blame it on Rio: Portugal's education minister, Tiago Rodrigues, was robbed at knifepoint while walking near Ipanema Beach. The thieves were caught and Rodrigues' belongings recovered.

In addition, organizing committee spokesman Mario Andrada said the bullet that flew through the roof of a media tent Saturday at the equestrian center came from a nearby slum. Andrada quoted the Defense Ministry as saying a suspect was “aiming at the police blimp which carried cameras. ... The Games weren't the target.”

Kenya merciless: Kenya said it would send its track and field manager home and show “no mercy” after allegations that he told undercover reporters posing as coaches he could protect doping athletes from drug tests in exchange for a payoff.

The secretary for sports, Hassan Wario, said Michael Rotich would face a police investigation.

“We will have no mercy,” Wario said.

Also:Dario Saric blocked Pau Gasol's shot just before time expired, preserving Croatia's 72-70 basketball upset of Spain. ... Italian Daniele Garozzo stunned top-ranked American Alexander Massialas to win gold in men's foil fencing.