The King Islander's time of 3:48.37 in the Svein Arne Hansen Dream Mile broke the Australian and Oceania records set by Craig Mottram on the same Oslo track 16 years ago.

The 22^nd fastest mile of all time, it was a personal best by a huge 2.24 seconds and adds to McSweyn's national records over the indoor equivalent plus the 3000m, 10km and 1500m which he is now focusing on for Tokyo.

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The Launceston-born, Melbourne-based 26-year-old was delighted with both the victory and time just a month out from his Olympic debut.

"I am very happy," he said.

"My season is going in the right direction going into the Olympics. I want to try and stay healthy going into Tokyo. I still have a few things to work on.

"I felt in good shape going into tonight and this proved that."

McSweyn is already confirmed on the Australian Olympic team with qualifying times for the 1500, 5000 and 10,000m.

He ran the 5000-10,000m double at the 2018 Commonwealth Games but has asked Athletics Australia to nominate him only for the shorter distance in Tokyo.

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"The 1500m is going to be a really tight competition but I am confident going into it. I did consider doubling up with the 5000m but the heats are all too close together and I don't feel strong enough yet for that."

The athletic program in Tokyo did McSweyn few favours with round one of the 1500 and 5000m both on Tuesday, August 3.

Six months after setting an Australian all-comers record of 3:50.61 for the mile in Penguin, McSweyn's performance in the Bislett Stadion drew widespread acclaim.

UTAS Athletics Club called it "one of his finest performances on the world stage".

It added that McSweyn's lead-up to Tokyo could not have gone better, with a 3:31.57 1500m at the Doha Diamond League meet placing him third on the world rankings for 2021.

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"This morning's race in Oslo is not only an all-time best by an Australian, it is the fastest time in the world since 2014 and one of the best times ever produced by any athlete," said UTAS AC's executive officer Tracy Canham.

Under the guidance of coach Nic Bideau at Melbourne Track Club, McSweyn's performances saw him named Australian Athlete of the Year by Athletics Australia in April.

Bideau said: "He had a plan last night to put it to them once the pacemakers were gone - and he executed that really well."