Ariarne Titmus concedes she doesn’t know what the future holds beyond the Paris Olympics as the Australian swimming star attempts to make the most of her time at the top.

The Olympic champion whipped through Tuesday night’s 400m freestyle final in 3 minutes 58.47 seconds in the Australian trials at Melbourne Sports and Aquatic Centre ahead of next month’s meet in Japan.

There, she is prepared to embrace the “underdog” tag against 16-year-old sensation Summer McIntosh, who took the world record from Titmus by clocking 3:56.08 in March, and American great Katie Ledecky.

Titmus, 22, didn’t swim as fast as she’d hoped for in Melbourne, though she didn’t fully taper and admitted she and coach Dean Boxall had pondered whether she might be into her final handful of 400m events at her peak.

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“When you’re going into a meet like this you always want to take an opportunity to swim as fast as you can,” she told reporters.

“Dean and I had the conversation. I don’t know what I’m gonna do after Paris – like I plan to continue but you never know – and this could be like my fourth-last 400m including Paris and trials and then worlds and this.

“If I decide to end, it could be my fourth-last rested 400. So you’ve got to use these opportunities to swim as fast as you can.

“Honestly, I wanted to swim a bit faster tonight, but I’ll look at the splits and see how it went.”

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Titmus somewhat then backtracked on her comments, saying: “I kind of regret now saying that because now you will think I’m gonna quit but I’m not” and stressed she couldn’t think beyond the current Olympic cycle.

“I’m still quite young,” she said.

“But just looking in the scheme of things like in the lead-up to Paris we were saying that this could be one of my last opportunities to really swim fast. This meet, worlds, trials and Olympics.

“(It’s) certainly not a love thing or a body thing. I think if I went to Paris and won again, certainly like a motivational factor.

“Like it becomes harder to keep training at the same level when you have essentially achieved everything you’ve wanted to achieve.”

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Lani Pallister finished second on Tuesday night in 4:02.43 and also qualifies for the Australian team.

The hotly anticipated men’s 400m freestyle proved a thriller.

Young gun Sam Short 3:43.38 just held off reigning world champion Elijah Winnington (3:43.48) to touch the wall first, in potentially a preview of the final in Fukuoka.

Veteran and local hope Mack Horton (3:46.71) came third.

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Earlier, Kaylee McKeown claimed the 200m individual medley to seal her ticket to the world championships but fell short of breaking Stephanie Rice’s long-standing Australian record of 2:07.03.

McKeown, who didn’t taper, notched 2:07.60 while second-placed Jenna Forrester (2:09.29) also qualified.

Emma McKeon won the 100m butterfly in 56.74 while Brianna Throssell (57.66) also sealed her spot on the team.

Zac Stubblety-Cook won the 100m breaststroke in 59.68.

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The 200m breaststroke specialist will make the team for Japan after breaking the FINA time of 59.75 but second-placed Sam Williamson (59.82) fell short.