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.”
Jones' dream of making history with a third consecutive Gold ended in a shock first round defeat.
Olympic Refugee Team representative Kimia Alizadeh produced an accomplished performance to beat Team GB's double Olympic champion 16-12 - despite not having competed since 2018.
There was late drama as the British team challenged points awarded to Kimia for a kick which they thought may have landed outside the ring.
But the appeal was rejected and it marked the end of Jones' Olympic reign. She must wait to see if Kimia goes on to claim her Olympic title to see if she gets an opportunity to fight again for bronze.
She cut a forlorn figure as she walked from the Makuhari Messe Hall in Tokyo, as did her teammates, including Bianca Walkden, who were there in the stands to cheer her on.
Jones, 28, had a two-point lead going into the final round but could not sustain her advantage and eventually lost 16-12 to Alizadeh, who won bronze in Rio.
For an opening bout at the Olympics, it was as tough as they come. Alizadeh was also a two-time world medallist.
She defeated Jones in Russia in 2015, but then left her native Iran to train in Germany, a decision which meant she was not seeded in the women's -57kg category.
Two three-point head kicks had given Jones an early lead, scoring twice to the body to turn the contest in her favour at the end of the second.
Team GB taekwondo world champion Bradly (c) Sinden, 22, of Doncaster, won his opening -68kg bout 53-8 against New Zealand's Tommy Burns to move into the second round.
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."
