Swimming great Michael Phelps calls it a day at at the Olympics on Saturday while the Rio curtain rises on another legend as sprinter Usain Bolt guns for three golds.
Jamaican Bolt enters the Rio fray in the heats of the men's 100m while Phelps, the most decorated Olympian in history, is expected to clinch the 23rd gold medal of his career in the 4x100m medley.
Both Phelps and Bolt have announced that Rio will be their last Olympics and the American is expected to end his career on a high note following his shock defeat on Friday to Singapore's Joseph Schooling in the 100m butterfly.
For Bolt the target is a third treble of the 100m, 200m and 4x100m relay golds.
Phelps, 31, was graceful in defeat to Schooling, 21, on Friday. He called the result 'kind of cool' after he was relegated to a three-way dead heat for silver with South African Chad le Clos and Hungary's Laszlo Cseh.
Singapore exploded in celebration in response to Schooling's win, the first gold medal in the country's history.
Schooling, who was inspired to become a top-level swimmer by a meeting with Phelps as a 13-year-old, set an Olympic record of 50.38sec.
"He said 'good job, that was a great race'," Schooling told of Phelps's reaction.
Another new generation swimmer, Katie Ledecky, completed the first 200m, 400m and 800m freestyle treble since 1968 -- and with a world record.
America's latest swimming sensation won the 800m in 8min 04.79sec, inside her seven-month old record of 8:06.68.
Phelps has insisted there is no way he is changing his mind about quitting after his fifth Olympics. And Jamaican hero Bolt has said he will also give up after these Games.
The 29-year-old world record holder will start the 100m heats on Saturday in preparation for a predicted showdown with US rival Justin Gatlin in the Olympic stadium on Sunday.
While Bolt's superstar status is unblemished, Gatlin, the world's fastest man this year, is still seeking to redeem his name after two doping bans.
The athletics has already produced one startling result -- a world record in the women's 10,000 metre for Ethiopia's Almaz Ayana.
Eyebrows were raised about the way in which Ayana smashed the record that has stood for 23 years, by nearly 14 seconds with a time of 29 min 17.45 sec.
"I praise the lord, the lord gives me everything," she said through an interpreter when asked about the performance. "My doping is my training, my doping is Jesus -- otherwise I'm crystal clear."
Athletics is battling a torrent of doping controversies after world body the IAAF suspended Russia's track and field team.
Also in track and field Michelle Carter of the United States stunned defending champion Valerie Adams of New Zealand with her very last throw to win the gold medal in the women's shot put.
Wang Zhen of China won the men's 20km race walk gold, 15 seconds ahead of compatriot Cai Zelin.
Britain's Jessica Ennis-Hill leads Belgium's Nafissatou Thiam by 72 points in her bid to retain the heptathlon title. She won the 100m hurdles, finished third in the high jump and second in the shot put and 200m.