Swimming returned to NBC’s primetime coverage of the Olympic Games with the first of eight straight days of finals Saturday. The United States won six medals, its first of the Tokyo Olympics, in the pool. A world record was also broken in the evening's final event.
The first four sets of swimming medals were on the line in the men’s 400m individual medley, men’s 400m freestyle, women’s 400m IM and women’s 4x100m relay. Relive the action below with highlights from the Tokyo Aquatics Center.
SEE MORE: Simone Manuel, after missing out on 100m free, tabbed to anchor U.S. relay
Men's 400m IM - Final
The United States is off an running in the best possible way.
The Americans swept gold and sliver, with Chase Kalisz, the Rio 2016 silver medalist, executing arguably the best race of his career to clinch gold and Jay Litherland closing hard in the final 50 meters to complete the 1-2 finish.
Kalisz turned at the 300-mark nearly 2.5 seconds ahead of top-seeded Kiwi Lewis Clareburt, who usually closes well. On commentary at that moment, Michael Phelps, a longtime friend and former training partner of Kalisz's, called it "The closest 400 IM I think I've ever seen."
But that comment would prove to be premature, as Kalisz won by over three-quarters of a second.
"It mean's the word," Kalisz said through the pain of lactic acid buildup. "This was the last thing I really wanted to accomplish in my swimming career. This is something that's been a dream of mine for as long as I can remember."
Litherland, who was born in Osaka, Japan, was behind significantly heading into the final 50, but closed exceptionally well to take silver
SEE MORE: Chase Kalisz talks 400m medley gold: 'I did it'
Women's 100m butterfly - semifinals
Marie Wattel of France and Zhang Yufei of China won both semifinal heats, with Zhang emerging as the top seed with a time of 55.89.
Australia's Emma McKeon and Sweden's Sarah Sjostrom advanced as the next fastest swimmers, while Torri Huske will be the lone American in the final.
Men's 400m freestyle - Final
Tunisia's Ahmed Hafnaoui shocked the Tokyo Aquatic Center, winning the men's 400 free from Lane 8 in 3:43.36.
Australia's Jack McLoughlin took silver, while American Kieran Smith touched for bronze.
SEE MORE: Tunisian swimmer stuns with Lane 8 win in 400m freestyle
Women's 400m IM - Final
Japan has is first swimming gold medal of the Tokyo Games. Ohashi Yui could not be caught despite charging efforts from both Americans in the pool. Ohashi finished in 4:32.08.
Emma Weyant took silver in 4:32.76 and Hali Flickinger completed the podium over two seconds later for Team USA's fifth medal of the evening.
Mireia Belmonte (ESP) and Katinka Hosszu (HUN) with eight Olympic medals between them, finished off the podium in fourth and fifth, respectively.
SEE MORE: Japan's Ohashi wins 400m IM; Americans take silver, bronze
Men's 100m backstroke - semifinals
Great Britain's dominant breaststroker Adam Peaty set a predictably quick pace, advancing as the top seed by a half-second.
Both Americans in the event, Michael Andrew and Andrew Wilson, advanced to the final.
SEE MORE: Adam Peaty dominates 100 breast semi, USA's Andrew advances
Women's 4x100m Freestyle relay - final
Australia claimed the first world record of the Tokyo Olympics, breaking their own mark set three years ago. At 3:29.69, they are the first to ever break three and a half minutes in the women's 400 relay.
Emma McKeown's 51.35 leg was fastest, joining sisters Cate and Bronte Campbell and Harris Meg on the top step of the podium.
The duel for silver came down to the touch as Canada's Penny Oleksiak beat out Simone Manuel for Team USA by three hundredths of a second. In Rio, that pair tied for gold in the women's 100m freestyle.
SEE MORE: Australia's world record wins 4x100 free relay, USA third
