|Olympic Games on the BBC|
|Hosts: Rio de Janeiro Dates: 5-21 August Rio time: BST -4|
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Andy and Jamie Murray are out of the Rio 2016 men's doubles after losing 7-6 (8-6) 7-6 (16-14) to Brazilian pair Thomaz Bellucci and Andre Sa.
The Murrays saved six match points, and wasted five set points, in an epic second-set tie-break before Bellucci and Sa eventually completed the win.
Earlier, defending champion Andy Murray won his opening singles match, beating Serbia's Viktor Troicki 6-3 6-2.
British women's number one Johanna Konta beat Stephanie Vogt 6-3 6-1.
The 25-year-old 10th seed had to see off two break points in the first set before taking control against the world number 290 from Liechtenstein.
Men's world number one Novak Djokovic was beaten 7-6 (7-4) 7-6 (7-2) by Argentina's Juan Martin del Potro.
'Trying to win another medal builds the pressure'
After losing his serve in the first game against Troicki, second seed Murray, 29, went on to control the tempo of the match and says he is not feeling any pressure to win the singles title he claimed at London 2012.
"I will always keep my gold medal," he said. "That will always be there. You don't have to give it away.
"So, it's more trying to win another medal. That builds the pressure, and wanting to do something here. It's sort of the pressure I am putting on myself. I'm not thinking about four years ago.
"Having the Olympics come so soon after Wimbledon for me, it may have been easy to have a bit of a lull, but that's not going to happen with the Olympics."
Konta is hoping to cap a remarkable year - in which she has earned a career-high world ranking of 13, won a first WTA title and reached the Australian Open semi-finals - with an Olympic medal.
"It was a very tough match. She was playing inspired tennis and had nothing to lose," Konta said after winning on her Olympic debut.
Williams and Nadal through
Defending women's champion Serena Williams started her title defence with a 6-4 6-2 victory over Australia's Daria Gavrilova.
German second seed Angelique Kerber, who was beaten by American Williams in last month's Wimbledon final, won 6-3 7-5 in her opener against Colombia's Mariana Duque-Marino.
Rafael Nadal, the men's singles champion at Beijing 2008, is also through after beating Argentina's Federico Delbonis 6-2 6-1 on his comeback from injury.
The Spaniard had not played for two months after pulling out of the French Open with a wrist injury.
"The wrist needs little bit more time to be 100%," the 14-time Grand Slam winner said. "If this was not the Olympic Games, I would not be here competing."