American Michael Phelps won his 20th career Olympic gold medal on Tuesday, holding off a challenge from Japan's Masata Sakai to win the men's 200-metre butterfly, and later returned to win his 21st gold in the 4x200m freestyle relay.
Phelps is the most decorated Olympic athlete in history and built on his legend in Rio with a dramatic victory over Sakai and Hungary's Tamas Kenderesi. Just over an hour later - and with a medal ceremony in between - he anchored the United States in a convincing relay win over Britain and Japan.
In another thrilling race over 200m, American teenager Katie Ledecky won thefreestyle to maintain her bid to match Debbie Meyer's 1968 record of sweeping the discipline in 200m, 400m and 800m. Ledecky already has the 400m title and is strongly favoured to add the 800m crown on Friday.
And Hungary's Katinka Hosszu also expanded her collection of Rio gold with victory in the women's 200m individual medley.
But there was no doubt the night belonged to the 31-year-old Phelps and not only because he became the oldest man to win an individual swimming title at the Games.
The butterfly specialist was out to regain the title he won in 2004 and 2008 before losing on the touch to Chad le Clos four years ago in London after leading from the 50m turn.
"I was pretty fired up after that race," he said his delighted celebrations. "This is the race I really wanted tonight. I really wanted that one back.
"That last 10 metres were not fun. Oh my gosh, I thought I was standing still."
Phelps couldn't quite shake his pursuers though and, after Le Clos faded, Sakai threatened in the closing metres to draw level or even overtake him. This time there was to be no repeat of 2012 and Phelps won by four hundredths in 1 minute 53.36 seconds. Le Clos finished out of the medals in fourth as bronze went to Tamas Kenderesi of Hungary.
While Phelps is likely approaching the end of his legendary career, moments earlier compatriot Ledecky had taken another step of her own towards greatness.
She won in 1:53.73 for her second gold of the Games, and third overall, over Sweden's Sarah Sjostrom, who was herself chasing her second gold in Rio. Ledecky has never lost an international individual final and, despite losing to Sjostrom in the semi-finals, was comfortable in winning by 0.35 seconds.
"It was a really tough race but a lot of fun," Ledecky said. "It's amazing to get another medal.
"Once I hit the water I was on auto-control. I got in the lead and wasn't about to let it go."
World record holder Federica Pellegrini missed out on the medals as Australian Emma McKeon snatched the bronze.
The final individual medal went to Iron Lady Hosszu, who dominated from the first leg and was never in danger of not adding to the 100m backstroke and 400m medley titles won earlier in the week. She finished in an Olympic record of 2 minutes 6.58 seconds.
"I'm so excited to get the gold, I can't even believe it," Hosszu said. "I can't believe I have three golds."
Britain's Siobhan-Marie O'Connor was second, three tenths of a second behind, while bronze went to American Maya Dirado.
The session ended with Phelps returning to anchor the US relay team to a simple victory, which brought him his 25th overall Olympic medal.
Conor Dwyer, Townley Haas and Ryan Lochte had laid the foundation for the victory by handing Phelps a lead of well over a second for the final leg and he saw out the win in 7 minutes 0.66 seconds.
"Doing a double like that is a lot harder than it once was," he joked.
Britain took silver more than two seconds back, with bronze going to Japan.
In the semi-finals, reigning champion Nathan Adrian of the US progressed easily in first after claiming the final qualifying spot in the afternoon heats. Marcelo Chierighini of Brazil delighted the home crowd by sneaking into the final in eighth.
Australian Madeline Groves topped the women's 200m butterfly and in the men's 200m breaststroke Japan's Ippei Watanabe topped the sheets, having set a new Olympic record.