Bethany Shriever claimed a thrilling BMX gold for Great Britain moments after Kye Whyte took silver as Duncan Scott extended his medal streak in the pool in Tokyo.
Whyte's silver in the men's race was Britain's first at an Olympic Games, and a first gold quickly followed through Shriever in the women's event.
Scott claimed his third medal in Tokyo with silver in the men's 200m individual medley, while Luke Greenbank took 200m backstroke bronze.
Bryony Page, a silver medallist at Rio 2016, won bronze in the women's trampolining.
The men's eight also took bronze as GB finished the Games with two rowing medals.
It is their lowest rowing medal tally at an Olympics since they won two at Atlanta 1996, and the first time they have not won at least one gold since 1980.
Friday brought the start of the athletics in Tokyo, with Dina Asher-Smith qualifying second in her opening 100m heat.
From crowdfunding to Olympic gold
Shriever had to fund her own qualification campaign after UK Sport cut its support for her event following Rio 2016, and two years ago she said she needed to raise a "worrying" £50,000 through crowdfunding.
The 22-year-old, who also worked part-time as a teaching assistant to cover training costs, held off two-time Olympic champion Mariana Pajon from Colombia to win on her Olympic debut.
"Honestly, I'm in shock. To even be here is an achievement in itself," said Shriever.
"To make a final is another achievement in itself. To win a medal, let alone a gold medal, I'm over the moon."
Shriever's gold meant GB became the third country, after France and the Netherlands, to win in all four cycling disciplines - BMX, mountain bike, road and track.
Whyte finished 0.114 seconds behind Dutchman Niek Kimmann to claim silver.
Nicknamed the Prince of Peckham, 22-year-old Whyte has fought back from serious injury to earn his place on the Olympic podium.
Great Scott eyes GB history
Scott added to his 4x200m freestyle relay gold and 200m freestyle silver by finishing 0.28 seconds behind China's Wang Shun in the 200m medley.
Although Scott again narrowly missed out on a first individual gold, he could become the first British Olympian to win four medals at a single Games when the 4x100m medley takes place this weekend.
"It was always going to be tight and always going to be exciting. I am really happy with the swim," the 24-year-old Scot told BBC Sport.
Scott's silver came shortly after Greenbank took bronze in the 200m backstroke, describing his first Olympic medal as a "dream come true".
The 23-year-old touched home in 1:54.72 as Russian Evgeny Rylov won gold with an Olympic record 1:53.27.
"It is amazing," Greenbank told BBC Sport. "I am so happy - over the moon and a bit lost for words, I am not going to lie."
Scott and Greenbank took GB's swimming medal tally at Tokyo to six - three golds, two silvers and one bronze.
In the rowing, GB men's eight took bronze in the final race of the Tokyo 2020 regatta, pipped to silver by Germany as New Zealand took gold.
Vicky Thornley was edged out of a medal despite a late push in the women's single scull, with the 33-year-old finishing 0.67 seconds off bronze.
That was Britain's sixth fourth-placed finish at the Sea Forest Waterway, while they won two medals.
They were the leading rowing nation at Beijing 2008, London 2012 and Rio 2016, claiming six, nine and five medals respectively at those Games.
Athletics under way in Tokyo
Asher-Smith, who is bidding to become the first British woman to win an Olympic individual sprint gold, reached the semi-finals with a run of 11.07 seconds.
Daryll Neita and Asha Philip finished second in their heats to qualify for Saturday's semi-finals.
Jemma Reekie, Keely Hodgkinson and Alex Bell are into the women's 800m semi-final, while high jumper Tom Gale reached the men's final with a season's best of 2.28m.
There will be British interest in the men's 10,000m final at 12:30 BST on Friday with Marc Scott and Sam Atkin competing.
What's coming up on Friday?
Women's football reaches the quarter-final stage with GB taking on Australia at 10:00.GB face the USA in the women's rugby sevens quarter-finals at 10:30.Team GB's Bryony Page, a silver medallist in Rio, is currently in the women's trampoline final.Bradley Forbes-Cryans will race for GB in the canoe slalom K1 final (08:00).In judo, GB's Sarah Adlington makes her Olympic debut in the women's +78kg category (09:00-11:50).In hockey, GB's men face Belgium at 13:15.
