Helen Glover's defence of her Olympic rowing title got off to a shaky start alongside Polly Swann while the first gold medal of Tokyo 2020 was won by China in the shooting.
British duo Glover and Swann finished third in their heat in the women's pairs, some way off the pace but enough to ensure their berth in Tuesday's semi-finals.
China's Yang Qian shot an Olympic record score of 251.8 points to win the women's 10m air rifle.
Team GB's Andy Murray and Joe Salisbury got off to a promising start in the men's doubles, beating French second seeds Pierre-Hugues Herbert and Nicolas Mahut 6-3 6-2.
But blink and you've missed Tokyo's youngest competitor, Syrian 12-year-old Hend Zaza, who exited the women's table tennis tournament in the opening round - but made sure she snapped a selfie with winner Liu Jia to mark the occasion.
What else has happened in the early hours? Let us fill you in.
GB badminton players Marcus Ellis and Lauren Smith won their opening mixed doubles match, beating France's Thom Gicquel and Delphine Delrue 21-18 21-17.In tennis, Heather Watson is out of the women's singles in the opening round.Shooter Seonaid McIntosh finished 12th in the women's 10m air rifle qualification, missing out on the final, on her Olympic debut.Ashley McKenzie, GB's only male judoka in Tokyo, was eliminated from the Games in his first fight.'Not our perfect row' for Glover & Swann
Glover has become the first British mother to row at an Olympics but her impressive comeback to the Games has not been smooth-sailing.
Her defeat with Swann in the heat - won by Australia - was Glover's first for more than a decade, a run spanning 51 races and including Olympic golds in 2012 and 2016.
"It wasn't our perfect row but I guess there's value in learning in the early rounds," she said. "We're open to what's going to come next."
Elsewhere for GB's rowers, the men's four - bidding for its sixth consecutive gold in the event - won their heat to progress to the final. The quartet of Ollie Cook, Matt Rossiter, Rory Gibbs and Sholto Carnegie are all making their Olympic debuts and have got big shoes to fill.
Emily Craig and Imogen Grant are into the semi-finals of the lightweight double sculls, but the women's four and men's eight must go again in the repechages if they are to reach the finals after finishing fourth and third in their heats respectively.
Murray and Salisbury win but Watson out
Murray and Salisbury's doubles partnership is a new one but one that seems to have gelled nicely, as they eased past the French Open champions.
Murray is the defending two-time Olympic champion in the men's singles and won silver in the mixed doubles at London 2012 with Laura Robson, while Salisbury is making his Olympic debut.
They will play Germany's Tim Puetz and Kevin Krawietz next for a place in the quarter-finals.
But it was an early exit for Watson, who lost 7-6 (7-5) 6-3 to Germany's Anna-Lena Friedsam.
Jamie Murray and Neal Skupski face Argentina's Andres Molteni and Horacio Zeballos later.
A warning for athletes
Olympics Games executive director Christophe Dubi has warned athletes they will be punished if they ignore anti-Covid measures.
It follows Friday's opening ceremony in which most of the Kyrgyztan and Tajikistan team members along with Pakistan's two flag bearers did not wear masks.
Athletes are required to wear masks at all times, except for when training, competing, eating or sleeping.
One more athlete has tested positive for Covid-19. They are the 12th competitor to return a positive test in Tokyo, while there have now been 123 cases in total.
There are also concerns about the heat in Tokyo, after a Russian archer fainted in intense heat during Olympic qualifying on Friday and the rowing schedule was changed.
Temperatures reached 33C in the archery dome on FridayWhat's coming up?
The men's road race continues, with Tao Geoghegan Hart, Geraint Thomas, Adam Yates and Simon Yates competing for Team GB.It's men's qualification day in the men's artistic gymnastics. Max Whitlock, Joe Fraser, Giarnni Regini-Moran and James Hall are GB's quartet (06:30 BST).Team GB's men's hockey players begin their Olympic campaign against South Africa (10:30 BST).GB women's football team face hosts Japan in their second group game (11:30 BST).Adam Peaty begins the defence of his 100m breaststroke title in the swimming pool (12:40 BST).
