(Reuters) - Surprise wins and misses dominated the Olympic storyline on Sunday as new champions from unlikely nations joined traditional powerhouses atop medal podiums and stars faltered.
Here's what you need to know about the Tokyo Games:
POOL OF DREAMS
Tunisia's Ahmed Hafnaoui not only stunned swimming superpowers with his gold medal performance in the 400m freestyle - he didn't quite believe the result himself.
"I was so surprised I didn't accept that," he told a news conference, where he was mobbed by reporters and inundated by requests for selfies. "I just can't believe it. It's a dream and it became true. It was great. It was my best race ever."
Michael Phelps hailed Hafnaoui for his "unbelievable swim," saying the 18-year-old Tunisian's shock victory was a great example of how swimming at the Tokyo Games was likely to have a series of wide open races.
"The difference between these Olympics and the past, in my opinion, is that every single person in the final has a chance of winning gold – it doesn't matter if you are in lane one, eight or four, everyone is close," said Phelps, the most decorated Olympian of all time.
The first world record fell in the pool when Australia won the 4x100 women's freestyle relay Olympic gold for the third time in a row. The quartet of sisters Bronte and Cate Campbell, Meg Harris and Emma McKeon took 0.36 seconds off their previous best.
American Chase Kalisz won his country's first gold in the 400m individual medley with a swim of 4:09.42, leading an American one-two with Jay Litherland collecting silver.
It was a golden day for the host nation, which shared the lead with China for the most gold medals at the conclusion of events on Sunday. See the medal tally here https://graphics.reuters.com/OLYMPICS-2020/EXPLAINER/gjnvwnlwgpw/index.html#section-medals
Skateboarder Yuto Horigome, who grew up in the Tokyo ward where the event is being held, took gold at the Games debut of a sport once seen as a symbol of counter-culture.
In a nail-biting final, Horigome stumbled through the two initial runs, but regained his signature cool in landing four of the five final tricks, earning 9.50 for a nollie backside 270.
Swimmer Yui Ohashi held on to beat the Americans in the women's 400m individual medley.
Judoka Uta Abe triumphed in the women's 52kg category in Tokyo, hours before her brother Hifumi took gold in the men's 66kg final, making history as the first siblings to win gold medals on the same day.
Tennis player Kei Nishikori upset fifth seed Andrey Rublev 6-3 6-4 on home soil. Naomi Osaka powered through her opening match.
DREAM TEAM DOWN
The U.S. basketball team fell to France 83-76 on Sunday as the Americans suffered their first defeat since 2004 at the Olympics.
The French had upset the U.S. men when they last met in the 2019 FIBA World Cup quarter-finals and they had their number again on the first day of group play at the Saitama Super Arena, powered by a game-high 28 points from Evan Fournier.
When Annemiek Van Vleuten crossed the line with her arms in the air at the Fuji International Speedway, the Dutchwoman thought she had won the women's Olympic road race.
Only a few moments later, however, an emotional Van Vleuten realised she had finished second behind Austrian Anna Keisenhofer by a healthy margin of one minute and 15 seconds.
"Oh Ruud, I was completely wrong," Van Vleuten told her soigneur Ruud Zijlmans after the finish. "I didn't realise it at all."
Unlike the professional world cycling tour events, riders in the Olympic races cannot communicate with their team via radio and it appeared to be the undoing of Van Vleuten and her three teammates, who were not aware that the Austrian was up the road ahead of them.
World No. 1 tennis player Ash Barty spun out of the first round with a dismal defeat to 48th ranked Sara Sorribes Tormo.
Andy Murray withdrew with an injury before he started.
Golfing world number one John Rahm and world number six Bryson DeChambeau both tested positive for COVID-19 before their departure for the Games.
(Editing by Leela de Kretser)