Ariarne Titmus defeated Katie Ledecky in a thrilling women's 400 metre freestyle final that lived up to its billing, while the brilliant Adam Peaty made history by becoming a double Olympic champion.
A star-studded cast in the pool at the Tokyo Aquatics Centre on Monday did not disappoint, with Canada's Maggie McNeil adding to her World Championship title in the women's 100m butterfly.
And in the men's 4x100m freestyle relay, Caeleb Dressel – tipped to be one of the stars of the pool – earned his first gold of the Tokyo Games.
TITMUS AND LEDECKY PUT ON A SHOW
The only disappointment about the women's 400m free was the fact no fans were in attendance to witness a battle for the ages.
The pre-race hype centred around whether it would be Ledecky, who had never lost in an individual Olympic event, or Australia's world champion Titmus that would be prevail.
Ledecky held a six-tenths lead after 200m and looked well on course to defending the title she won at Rio 2016 in a world-record time of 3:56.46.
But Titmus came storming back and a stunning 28.67 split on the way home was enough to fend off Ledecky – whose 3:57.36 was her second fastest time in the 400m free.
Titmus' 3:56.69 is second only to Ledecky's world record and she becomes the third Australian to win gold in the event.
PERFECT PEATY DOUBLES UP
There was no world record over three races for Peaty but his utter dominance of the men's 100m breaststroke shows no sign of abating as he became the first Briton to ever defend an Olympics swimming title.
Five years on from winning gold in a world-record time at Rio 2016 (a benchmark he has since beaten twice), Peaty swam a 57.37 to stand atop the podium again ahead of Arno Kamminga – the only other swimmer in history to go under 58 seconds.
It was perhaps not quite the time Peaty, who had designs on another world record, wanted but it still represents the fifth fastest time in history and edged his previous season best of 57.39.
Peaty unleashed an almighty roar after his win and later said to BBC Sport: "I haven't felt this good since 2016. It just means the world for me.
"Thank you to the nation for being behind me. This victory wasn't mine - it was a great swimming team, my family, my friends."
Peaty is now only the second man to defend an Olympic breaststroke title, and just the fourth swimmer from Great Britain to win multiple golds in the Games.
Athens 1896 #Tokyo2020 @adam_peaty's victory means that #TeamGB maintains its record of winning at least one gold medal at every summer Olympic Games.— Team GB (@TeamGB) July 26, 2021
The only country to do so. pic.twitter.com/QDrHCqLBmB
Maggie McNeil completed a world and Olympic double in the women's 100m butterfly in an incredibly tight race.
The Canadian was down in seventh but propelled towards the front after a brilliant turn and managed to hold off China's Zhang Yufei to earn gold.
The top four all ranked inside the top seven swims in the 100m butterfly of all time, with McNeil's 55.59 the second fastest ever. Australia's Emma McKeon took third, with Torrie Huske of the USA just 0.1 off the podium.
DRESSEL UP AND RUNNING
America's big men's hope in the pool at these Games is Dressel, who has been touted as the successor to the legendary Michael Phelps.
The 23-year-old is top seeded in three individual events and raced in the first of potentially four relay events on Monday as the United States romped to victory in the 4x100m freestyle.
Joined by Blake Pieroni, Bowen Becker and Zach Apple, the US came home in a time of to 3:08.97, with Italy and Australian rounding out the podium.
Elsewhere, Duncan Scott of Great Britain went fastest in the men's 200m freestyle (1:44.60) semi-finals ahead of American Kieran Smith (1:45.07), while world record holder Ryan Murphy led the way in the 100m backstroke semis.
In the women's 100m backstroke semi-finals, Regan Smith set an Olympic record time of 57.86 and Tatjana Schoenmaker went quickest in the women's 100 breaststroke semi-finals ahead of rival Lilly King.