Action returns to the Tokyo Aquatics Center on Day 3 for the second batch of swimming finals. Medals are on the line in four events: the women's 100m butterfly, men's 100m breaststroke, women's 400m freestyle and men's 4x100m freestyle relay.

A matchup between Katie Ledecky and Ariarne Titmus in the 400 free headlines the session, with the dominant Adam Peaty competing in his signature 100 breast and Caeleb Dressel getting his Tokyo Games started on the U.S. relay also adding to the night's intreague.

Watch live on NBC in primetime, or stream the action on and on the NBC Sports app.

Women's 100m Butterfly - Final


In an absolute nail-biter, the top four swimmers finished within 0.14 seconds of each other as gold, silver and bronze were all decided right at the touch. 55.59 ended up as the gold medal-winning time.

Canada's Maggie MacNeil got her fingertips on the wall first, while China's Zhang Yufei just .05 behind for silver. 

Australia's Emma McKeon got in one one-hundredth ahead of American Torri Huske to round out the podium.

Men's 200m freestyle - Semifinals


All three top seeded swimmers emerged from the second semifinal as Great Britain's Scott Duncan, American Kieran Smith and Danas Rapsys of Lithuania went 1-2-3.

Duncan set the pace at 1:44.60 headed into the final.

Women's 100m Breaststroke - semifinal


In a semifinal upset, Lilly King failed to win a heat in major competition for the first time in six years. South Africa's Tatjana Schoenmaker touched first in the second semifinal in 1:05.07 and will be the top seeded swimmer in Monday's final.

King said she had plenty more "left in the tank" for the final, and was undeterred after getting beat.

In the first semifinal, Lydia Jacoby, the other American, beat out her competitors, including Russian athlete Yulia Efimova.

Men's 100m breaststroke - final


Adam Peaty's grip on this event remains. The world record holder and defending Olympic champion took gold in 57.37.

Arno Kamminga and Nicolo Martinenghi rounded out the podium, with the American Michael Andrew fourth.

Women's 400m freestyle - final

Men's 100m backstroke - semifinal


Ryan Murphy inched closer to defending his 100m backstroke gold medal, emerging as the top seed from the semifinal round in 52.24.

Two Russians will challenge him in the final, Kliment Kolesnikov and Evgeniy Rylov.

Australia's Mitch Larkin will also be among the medal contenders. He qualified third to the final in 52.76.

Women's 100m backstroke - semifinal


After the Olympic record fell three times in prelims, Regan Smith lowered it once more in the semifinal round, to 57.86.

Smith will be joined in a can't-miss final by Canada's Kylie Masse and Australia's Kaylee McKeown, who qualified second and third, respectively.

McKeown is the world record holder in the event, set last month at Australia's Olympic Trials.

Men's 4x100m freestyle relay - final


A tremendous swim from all four Americans Caeleb Dressel, Blake Pieroni, Bowe Becker and Zach Apple clinched gold in 3:08.97 ahead of Italy and Australia.

Apple's anchor leg was best of them all at 46.69, with Dressel's leadoff leg at 47.26 to give the United States the early lead. 

The final exchange between Becker and Apple nearly disqualified the U.S., had apple left his blocks .05 seconds later.

For Dressel, the relay is his first of a potential seven gold medals in Tokyo.