Controversial Chinese swimmer Sun Yang claimed his third Olympic gold medal with a win in the men's 200 metre freestyle at Rio 2016.
Sun, who topped the podium twice in London, edged out Chad Le Clos and Conor Dwyer on Monday.
Banned for a positive doping test two years ago, Sun has been at the centre of controversy in Brazil after finishing second to the outspoken Mack Horton in the 400m freestyle.
American teenager Lilly King took out the women's 100m breaststroke over Yulia Efimova, who has also tested positive previously.
Hungarian Katinka Hosszu made it two golds in Rio, adding the women's 100m backstroke title to her 400m individual medley crown.
Ryan Murphy broke an Olympic record to win the men's 100m backstroke.
Earlier in the night, Missy Franklin failed to qualify for the 200m freestyle final as Katie Ledecky advanced, while Michael Phelps reached the 200m butterfly final.
RACE OF THE DAY
Hosszu made a slow start on Monday, but the 27-year-old recovered for her second Games medal.
She was sixth at the halfway mark before responding in the final 50 to hold off American Kathleen Baker by 0.30 seconds.
Canada's Kylie Masse and China's Fu Yuanhui finished with bronze after a dead heat.
Only the two Olympic records fell on a quieter night in the pool.
Murphy beat the time set by fellow American Matthew Grevers in 2012 thanks to a time of 51.97secs.
King also set a new Games mark with a time of one minute and 4.93 seconds, topping Leisel Jones' 2008 record.
"I gave it everything and I wasn't good enough. I have been trying to wrack my mind around what's going on. I have to keep fighting and believing," - Franklin was left disappointed after failing to reach the final.
"The adrenaline is going so hard for me right now, I don't even feel tired just because I'm so excited. This means everything to me. I've been swimming for 16 years and to have it come to this is just a dream come true," - a predictably thrilled Murphy said after breaking the Olympic record.
Another four gold medals are up for grabs in the pool on Tuesday. Phelps will be eyeing his 20th Games gold in the men's 200m butterfly, while Ledecky targets victory in the women's 200m freestyle.