Record-breaking Michael Phelps extended his tally to 21 Olympic gold medals as he won individual and team titles on day four at Rio 2016.The American, 31, comprehensively beat defending champion Chad le Clos in the 200m butterfly before he helped the US win the men's 4x200m freestyle relay.
"That's a lot of medals," said Phelps. "It's just insane. It's mind-blowing."
British quartet Stephen Milne, Duncan Scott, Dan Wallace and James Guy won the silver in the relay.
Phelps began the evening by avenging 24-year-old Le Clos' victory over him at London 2012.
"I wanted that one back. I came into the pool tonight with a mission and the mission was accomplished," added Phelps.
He cruised to victory in one minute 53.36 seconds as the South African only managed to finish fourth.
Japan's Masato Sakai and Hungary's Tamas Kenderesi overtook Le Clos in the final 50 metres to take the silver and bronze medals respectively.
Phelps and Le Clos meet again in another latest instalment of their duel when they compete in the 100m butterfly later this week.
The American will also be trying to add to his gold tally when he goes in the 4x100m medley relay and 200m individual medley, also later this week.
"Looking forward to the rest of the week and I'm not even halfway done yet," he said.
But reclaiming the individual 200m butterfly title was Phelps' main target in Rio following his dramatic defeat in London four years ago.
That final was supposed to be his farewell to the sport, having already announced his intention to retire after the 2012 Games. He then came out of retirement in 2014.
"I told Bob [Bowman, his coach] when I came back how bad I wanted that 200m fly," said Phelps.
"That being my very first Olympic event, to be able to win it in my fifth Olympics is pretty special.
"It was really just going through the last 16 years. That event was my bread and butter. That was the last time I'll ever swim it.
"There wasn't a shot in hell I was losing that tonight. And, if I did, every ounce that I had was left in the pool.
"Just being able to see the number one next to my name again, one more time in the 200 fly, you couldn't have scripted it any better."
Phelps is the most decorated Olympian of all time and has won more than twice as many gold medals at the Games as the athlete second on the list, former Soviet gymnast Larisa Latynina (nine).
Phelps returned to the pool just over an hour after his individual triumph to compete in the relay alongside US team-mates Conor Dwyer, Francis Haas and Ryan Lochte.
The defending Olympic champions lost to Britain at the 2015 World Championships, but led from the early stages to win by 2.47 seconds and retain their crown.
AnalysisAdrian Moorhouse, 1988 Olympic 100m breaststroke champion:
"What a fantastic 200m butterfly race. Michael Phelps was awesome. I thought they were going to catch him but he pulled it off.
"You can call him the greatest of all time now. He's great. He's invincible."