American swimmer Michael Phelps took his personal tally of gold medals to 21 after another day of Olympic success that was, in his words, "awesome".
The 31-year-old claimed first place in the 200m butterfly before following it up with a second gold in quick succession as part of the USA 4x200m relay team.
"There wasn't a shot in hell I was losing that tonight," Phelps said. "I came into the pool tonight on a mission, and it was mission accomplished.
"I didn't know I only won by 0.04 until the awards' ceremony – but just seeing the number one next to my name just one more time in the 200m fly, I couldn't have scripted it any better.
"On the podium, I was going through the last 16 years. That event (the 200m butterfly) was my bread and butter. And this was the last time I will ever swim it. Having that come to an end is crazy to think about."
The rivalry between Phelps and Chad le Clos of South Africa dominated the build-up to the race, with the American's "death stare" becoming the subject of an internet meme.
Phelps had the last laugh as the South African, who took gold at the London Olympics in 2012, finished fourth behind Masato Sakai of Japan and Tamás Kenderesi of Hungary.
"I don't want him to win and I'm sure he doesn't want me to win," Phelps admitted. "But he is someone who is a good racer, he is not afraid to put it on the line.
"The kid has talent. And last 10m oh my gosh, I thought I was standing still. It's good for the sport to have a competitor like that."
Phelps can still add to his medal tally in the two events remaining on his Rio 2016 schedule. He will compete in the 200m individual relay on Wednesday before finishing his Olympic career with the 100m butterfly on Thursday.