PARIS - Swimmer Daniel Wiffen secured Ireland's first gold medal of the Paris Olympics, setting a new Olympic record en route to victory in the men's 800m freestyle final on Tuesday.

The 23-year-old surged home in the last 25 meters to touch the wall in seven minutes, 38.19 seconds, smashing Mykhailo Romanchuk's previous Games record by more than three seconds.

American Bobby Finke took silver in 7:38.75 and Italian Gregorio Paltrinieri claimed bronze in 7:39.38 at La Defense Arena.

"I always knew it (a gold medal) was going to come, I didn't know what event it was going to be in but I knew I was going to win one of them," a confident Wiffen said after the race.

"For it to be my first event is even better. I don't (know) how to sum it up, to be honest. Incredible."

Australia's Kaylee McKeown also established a new Games record as she won her second consecutive Olympic 100m backstroke title.

McKeown finished in 57.33 seconds, beating her own previous mark of 57.47 set in Tokyo three years ago. American world record holder Regan Smith took silver in 57.66 and her compatriot Katharine Berkoff claimed bronze in 57.98.

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"It feels surreal to be honest with you, and I wasn't sure if I'd be any good there tonight," McKeown said after the race. "I didn't put expectations on myself, I was going to get out and enjoy the atmosphere, and that's the best you can do for yourself."

"I knew it was going to come down to the last five meters. She (Smith) pushed me the whole way through. You wait for the race and finish it, and I can't even remember it now."

In the last medal race of the evening, Britain cruised to its second consecutive Olympic men's 4x200m freestyle relay title by holding off challenges from the United States and Australia.

Britain's team of James Guy, Tom Dean, Matthew Richards and Duncan Scott led at every turn to finish in six minutes, 59.43 seconds.

The United States' combination of Luke Hobson, Carson Foster, Drew Kibler and Kieran Smith took silver, more than a second further back.

Australia's Maximillian Giuliani, Flynn Southam, Elijah Winnington and Thomas Neill claimed bronze.

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"We worked very hard for this and it's nice to be rewarded with the gold medal," an elated Guy said after the race.