Katinka Hosszu made history on Saturday by setting a new world record in the women's individual medley, while Australia's Mack Horton won the men's freestyle and Japan won gold and bronze in the men's individual medley.
Hungary's Katinka Hosszu made history on Saturday, picking up gold in the 400m individual medley and setting a stunning new world record. Maya Dirado of the United States finished second while Spain's Mireia Belmonte claimed bronze.
Hosszu's time of four minutes 26.36 seconds comfortably smashed the previous record held by China's Ye Shiwen. The feat is the largest jump in a world best since Tracy Caulkins won by 9.06 seconds at the Los Angeles games in 1984.
The Olympic gold medal is a first at this level for the 27-year-old Hungarian after four attempts, despite holding the current title of world champion and winning nine medals at three different world championships.
Known as "The Iron Lady", Hosszu led the entire race and even had time to turn and enjoy her victory before her opponents finished.
Japan double in individual medley
Japan picked up its first gold medal in swimming of the Rio Games on Saturday, after Kasuke Hagino won the men's 400 meter individual medley.
The United States' Chase Kalisz had been the favorite going in to the showdown, having been the fastest in the heats, yet he was forced to accept second place, while Japanese swimmer Daiyo Seto claimed bronze.
Hagino won with a time of four minutes 0.65 seconds after finishing third in the event in London four years ago. The swimmer's achievement means he is the first non-American to win the event since 1996 and the fastest ever to reside from outside of the United States. It was also the third fastest ever.
Horton overcomes China's Sun Yang
Australia picked up gold in the men's 400 meter freestyle after Mack Horton managed to beat Sun Yang of China, while Gabriele Detti picked up Bronze for Italy.
With a time of three minutes 41.55 seconds, Horton dethroned Sun Yang, who won the event in London four years ago, by just 13 tenths of a second.
Known as bitter rivals, Horton and Yang didn't even acknowledge one another after the race. Despite climbing out of the pool side by side, both athletes ignored one another as Horton walked off to celebrate.
Sun had previously served a three-month suspension for using a banned stimulant, which Horton was more than happy to reference earlier in the week. When asked about the frosty reception between the two, he told reporters: "He splashed me to say hello, and I didn't respond because I don't have time for drug cheats."
New world record for Peaty
British swimmer Adam Peaty broke his own world record of 57.55 and created a new Olympic record in the first heat of the 100m breaststroke. Peaty, a European and world champion, is competing at his first Olympic Games for Great Britain and set the previous record in the discipline at 57.92 in 2015.
Britain's Adam Peaty broke his own world record of 57.55 in the first heat of the 100m breaststroke.
Disappointment for Heidtmann
Germany's Jacob Heidtmann clocked in at 4:11,85, breaking his own record and the best national time, but was disqualified for using two dolphin kicks. Swimmers are only permitted to use one dolphin kick, and the 21-year-old was notably dejected with the outcome. American Chase Kalisz won the heat with a time of 4:8,12.
It was a frustrating day all around for Germany's swimmers with Alexandra Wenk missing out after competing in her first Olympic race in the 100m butterfly. Florian Vogel and Clemens Rapp missed the cut in the 400m freestyle.
Further gold for Australia in women's 4x100 freestyle
Australia capped off a wonderful night in the pools with gold in the women’s 4x100 meter freestyle relay, with the United States and Canada finishing second and third respectively.
Coming in at three minutes and 30.65 seconds, Australia overcame the mark they set two years ago to confirm a new world record. Furthermore, Brittany Elmslie, Emma McKeon and sisters Bronte and Cate Campbell compounded further defeat on the United States, who haven’t won the event since the 1996 games in Atlanta.
The result now means Australia have won more gold medals from swimming on day one of the Rio Games than they did in the whole of the London games.