Andy Murray and Jade Jones saw their gold medal defences come to an end in a double blow for Team GB at the Tokyo 2020 Olympics.
And Wimbledon champion Ashleigh Barty suffered a shock exit from the women’s tennis singles as she lost her first-round match.
Murray, the 2012 and 2016 Olympic champion, withdrew from the men’s singles on medical advice just hours before he was due on court.
Team GB’s medical staff warned the 34-year-old his reconstructed hip would not stand the rigours of playing in both singles and doubles tournaments.
And after he and Joe Salisbury launched their doubles campaign in style on Saturday, Murray decided his team-mate should take priority over personal glory.
“I am really disappointed at having to withdraw but the medical staff have advised me against playing in both events,” he said after pulling out ahead of his match against Felix Auger-Aliassime.
“So I have made the difficult decision to withdraw from the singles and focus on playing doubles with Joe.”
Taekwondo star Jones was also defending her titles from the London and Rio de Janeiro Olympics – bidding to become the first British woman to win at three successive Games.
But she was beaten by Kimia Alizadeh of the Refugee Olympic Team as she opened her gold medal defence in the -57kg category.
Jones could still have the chance to compete for bronze, as fighters whose opponents reach the final are given a second chance in the repechage.
Following Murray and Jones’ exits, there was a huge shock in the women’s tennis singles as world number one Barty was convincingly beaten by Spain’s Sara Sorribes Tormo.
Just weeks after her Wimbledon triumph, the Australian lost 6-4 6-3 – leaving home favourite Naomi Osaka as the highest-ranked player left in the women’s draw.
Earlier on day two of the Olympics, Britain’s Adam Peaty won his 100m breaststroke semi-final.
After he was critical of himself following his victory in the heats, gold medal favourite Peaty was happier with his semi-final performance.
“It was a little bit better, more controlled,” he told BBC Sport.
“Medals aren’t won in the heats or the semi-finals.
“Everyone has been so welcoming here. These are the Olympic Games – the greatest show on earth – so obviously we want to show a mutual respect.
“Olympics is always about racing. I’m the best racer in the world, I think, so I’m looking forward to it.
“I wanted to be a little bit quicker this morning but hey ho, it’s a morning swim.”