"It was certainly a tough race and I delivered. I couldn't do much better than that. It was my second-best swim ever (over 400m freestyle). I felt like I fought tooth and nail and that's all you can ask for," said Ledecky.

Australia has not won a medal in the women's 400m freestyle at the Olympic Games since Hayley Lewis took bronze in 1992.

"It is the biggest thing you can pull off in your sporting career, so I'm over the moon. I'm trying to contain it as much as I can. I have a big programme ahead of me, but I can enjoy this afterwards," Titmus commented after the win.

In the men's 100m breaststroke, Adam Peaty defended his title for Britain in 57.37 seconds. Arno Kamminga of the Netherlands won the silver in 58 seconds and Italy's Nicolo Martinenghi took the bronze in 58.33.

Peaty became the first swimmer representing Britain to win a specific event multiple times at the Olympic Games.

The finalists for men's 200m freestyle, men's 100m backstroke, women's 100m backstroke and women's 100m breaststroke were confirmed. Xu Jiayu won China a place in the men's 100m backstroke.

In women's 100m backstroke semifinals, Regan Smith qualified as the quickest by setting a new Olympic record at 57.86 seconds.

The United States, Italy and Australia finished 1-2-3 in men's 4x100m freestyle relay.