USA's Caeleb Dressel set an Olympic record on his way to winning the men's 100m freestyle gold medal as he seeks to become one of the most successful swimmers at an individual Games.
Dressel won in a time of 47.02 seconds to claim his second gold in Tokyo.
China took gold in a thrilling women's 4x200m freestyle in a world-record time of seven minutes 40.33 seconds.
Meanwhile Great Britain's Commonwealth champion James Wilby missed out on a medal in the men's 200m breaststroke, reports the BBC.
He was second fastest in the semi-final and started well in the final before fading.
Australia's Zac Stubblety-Cook broke an Olympic record to win the race with a time of 2:06.38 seconds, finishing ahead of Arno Kamminga of the Netherlands and Finland's Matti Mattsson.
"Physically and mentally it hurts," Wilby told BBC Sport.
"The result is what it is. It is hard, the way I swim it has to be a perfect balancing act and if I am off ever so slightly it really pays off in a bad way."
Dressel edges thriller for second gold
It is Dressel's second gold of the Games after he helped USA win the 4x100m relay, but it was a close race as Australia's Kyle Chalmers finished just 0.06sec adrift with Russian Kliment Kolesnikov in third.
Dressel could finish this Olympics as one of the most successful swimmers at an individual Games as he is in contention for a further four medals - two individual (100m butterfly and 50m) and two in relays (medley and mixed medley).
Only two swimmers in Olympic history have won more than six medals at a Games - Michael Phelps with eight in Beijing in 2008 and Mark Spitz with seven in Munich in 1972.
"There's been a lot of pressure on me, there's nothing wrong with pressure but there is with stress. I handled it well and I am happy," Dressel told BBC Sport.
Dressel's United States team-mate Robert Finke won a surprise gold in the men's 800m freestyle final.
He came out of nowhere in the final 75m to pip world champion Gregorio Paltrinieri by 0.24 seconds, while Mykhailo Romanchuk took the bronze medal.