20-year-old Australian swimming sensation Ariarne Titmus outclassed American legend and reigning champion Katie Ledecky in the women's 400m freestyle at the Tokyo Aquatics Centre, in what was billed as one of the biggest upsets in the history of the sport at the Olympics.
Ahead of the final, the US superstar was expected to dominate the pool after her heroics in Rio, where she had won four gold medals.
But Titmus managed to upstage her idol, matching her stroke for stroke during the final 50m of her first race in the Japanese capital city.
Not only did Titmus accomplish a surprise win over Ledecky, her time of 3 minutes, 56.69 seconds is also the second fastest ever recorded in the women's 400m freestyle. Ledecky still holds the world record, with a time of 3:56.46
However, Ledecky is not the first athlete to experience a shock defeat at the ongoing Olympics in Japan. Take a look at the other biggest upsets in the quadrennial sports mega-event.
Ahmed Hafnaoui Claims Men's 400-Meter Freestyle Gold
18-year-old Tunisian Hafnaoui qualified as the last (eighth) swimmer, recording the slowest time ahead of the final. But he stunned the more experienced and accomplished swimmers to emerge victorious in the 400m freestyle event with a time of 3 minutes, 43.26 seconds.
Australia's Jack McLoughlin (3:43.52) and American Kieran Smith (3:43.94) took silver and bronze respectively.
"I surprised myself. It's unbelievable. I just can't believe it. I'm an Olympic champion now," Hafnaoui said after winning the race.
United States' 25-Game Winning Streak in Basketball Comes to an End at the Olympics
The American men's basketball team suffered a surprise 83-76 loss to France at the Saitama Super Arena near Tokyo on Sunday.
It was the US men's team's first loss since the 2004 Olympics in Athens and their sixth defeat ever at the grand sports event.
The loss also ended their 25-game winning streak, which started way back in 2004 and included three consecutive gold medals in Beijing, London, and Rio.
Dating back to 1936, the US is the most successful team in basketball, with 15 gold medals.
They have failed to win the gold only once, and that was in 2004, when the team comprising several NBA (National Basketball Association) stars suffered three unexpected defeats and could only secure a bronze medal.
Reigning Wimbledon Champion Ash Barty Exits Tokyo
Just two weeks after winning her second Grand Slam and her maiden Wimbledon title, Australia's Ash Barty was handed a first round defeat in Tokyo.
Barty, who is known for her consistency and immaculate ground-strokes, was unable to find her best form and rhythm, eventually suffering a 6-4, 6-3 loss to Sara Sorribes Tormo of Spain in her maiden appearance at the Olympics on Sunday.
"It was a tough day, a disappointing day. I can't lie about that," Barty told Australian media after her defeat.
Vishal Uppal, a former Indian tennis player, who participated in the Davis Cup for the country, acknowledged that Barty's departure from Round 1 of the Olympics came as a shock.
"Undoubtedly, Barty's defeat is a major upset because she was the firm favourite to win a gold medal in Tokyo, especially after her victory at Wimbledon earlier this month," Uppal told Sputnik on Tuesday.
Austria's Anna Kiesenhofer Stuns the Cycling World in Japan
Anna Kiesenhofer of Austria possibly caused the biggest upset in the history of cycling at the Olympics and arguably the greatest shock in Tokyo after she claimed the gold medal in the women's road race on Sunday.
Before the Olympics started, nobody knew anything about the 30-year-old Austrian rider as she wasn't expected to pose much trouble for the likes of two-time gold medallist and defending champion Anna van der Breggen, former world champion Annemiek van Vleuten, Britain's Lizzie Deignan, former Olympic bronze medallist Elisa Longo Borghini, and Lisa Brennauer of Germany.
But Kiesenhofer had other ideas as she never got overawed by the situation and managed to trump all of them during the 147-kilometre race to clinch her nation's first gold medal at the Olympics since the modern Games began in 1896.