Sydney McLaughlin obliterated her own world record to win Olympic gold in the women's 400m hurdles on Wednesday as Japanese teenager Sakura Yosozumi maintained the hosts' stranglehold on the skateboarding competition.
Canadian sprinter Andre de Grasse powered to gold in the men's 200m final, completing a long journey back from injury and illness after taking silver behind Usain Bolt in 2016.
And in cycling, Italy won the men's team pursuit for the first time in 61 years, breaking their own world record to beat Denmark in a thrilling final at the Izu Velodrome.
At the Olympic Stadium, McLaughlin powered home in 51.46 seconds, with defending champion Dalilah Muhammad claiming silver in 51.58 after another classic duel between the two dominant American hurdlers.
It repeated the feat of Karsten Warholm, who took a huge slice off the world record in the men's race just 24 hours earlier.
The 21-year-old McLaughlin's blistering time bettered her world record set at the US trials in Oregon in June, when she ran 51.90sec.
"I saw Dalilah ahead of me with one to go," said McLaughlin. "I just thought 'run your race'. The race doesn't really start till hurdle seven. I just wanted to go out there and give it everything I had."
De Grasse claimed his first major championship gold medal, racing home in 19.62sec with Kenny Bednarek of the United States second in 19.68 and reigning world champion Noah Lyles taking bronze (19.74).
"I've been waiting for this moment, I've been training hard for this moment," said De Grasse, finally delivering on his promise after suffering hamstring problems and a bout of mononucleosis following his breakthrough in Rio.
Canada's Damian Warner ended the first day of the decathlon in top spot, with fancied French rival Kevin Mayer in fifth after complaining of back problems.
Defending champion Nafi Thiam of Belgium tops the heptathlon standings with four events gone. British world champion Katarina Johnson-Thompson's medal hopes are over after she pulled up with a calf injury in the 200m.
Dutch star Sifan Hassan took the next step in her bid for an unprecedented treble, easing into the 1500m final two days after winning the 5,000 title.
Emmanuel Korir led home compatriot Ferguson Rotich for a Kenyan one-two in the men's 800m final, ahead of Poland's Patryk Dobek.
Rotich said: "In Kenya we are progressing despite the challenges of the pandemic.
"In the last year, most of us, we didn't train well. There was the coronavirus and now we're coming back."
Poland's Wojciech Nowicki bagged gold in the men's hammer. Norway's Eivind Henriksen claimed silver, with four-time world champion Pawel Fajdek, another Pole, taking bronze.
There was a first ever Olympic gold for a Ugandan woman as Peruth Chemutai won the 3000m steeplechase, with American Courtney Frerichs collecting silver and Kenyan Hyvin Kiyeng bronze.
Teen skateboard battle
Away from the athletics, Yosozumi won the women's park skateboarding event to stop compatriot 12-year-old Kokona Hiraki and Britain's Sky Brown, 13, becoming the Games' youngest-ever gold medallists.
The 19-year-old Yosozumi carved up the Ariake Urban Sports Park with a flowing opening run in the final, and her 60.09 points proved enough for victory ahead of Hiraki and Brown.
"This medal feels unreal — it feels like a dream," said Yosozumi, as she celebrated at a sun-baked Ariake Urban Sports Park.
"I hope skateboarding is going to be very popular in Japan because of the strong performances of the Japanese team," she said, adding: "Now I want to go back home and eat some delicious food."
In a sport making its Olympic debut, Japan also snapped up the men's and women's street titles earlier in the Games and they have now bagged five of the nine medals so far.
In the first round of the women's golf tournament, world number one Nelly Korda carded a four-under-par 67 to sit just one shot behind leader Madelene Sagstrom of Sweden.
The searing temperatures forced US star Lexi Thompson's caddie to pull out with heatstroke and organisers said the tournament could be cut to 54 holes because of an approaching tropical storm due to hit this weekend.
Away from the action, all 12 members of the Greek artistic swimming team are in isolation after five tested positive for coronavirus in the first cluster detected at the Games.
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