Australia's new golden girl Ariarne Titmus is on another collision course with American swimming great Katie Ledecky after heats of the 200m freestyle at the Tokyo Olympics.

Seven hours after the Australian pipped Ledecky in a gripping 400m freestyle final, the pair returned in different heats over the shorter distance.

Both cruised through, with Ledecky logging Monday night's fastest time of one minute 55.28 seconds.

Australia's Titmus (1:55.88) was fourth-quickest and rarely approached top gear while compatriot Madi Wilson (1:55.87) was third fastest into Tuesday's semi-finals.

Titmus and Ledecky had little time to rest after their race for the 400m gold medal became an instant Olympic classic.

The Tasmanian-born 20-year-old now based in Queensland has always been rated a genuine gold medal shot in the 200m as well, boasting the world-leading time in the event this year.

Titmus got within 0.11 seconds of Federica Pellegrini's world record at Australia's selection trials and the Italian only scraped into the Tokyo semis in 15th spot.

'I will have to do a completely different race and attack from the outside lane,' Pellegrini said, admitting racing with no crowds lacked atmosphere.

'I miss the public and its push,' she said.

American star Ledecky, a five-time Olympic champion, is also in the midst of a 1500m campaign.

Soon after her 200m swim, Ledecky's relentless program continued with a 1500m freestyle heat - which she duly won.

Australia's 1500m pair Maddy Gough and Kiah Melverton advanced into the final in seventh and eighth spots respectively - their times were 20 seconds outside Ledecky's.

In the men's 200m butterfly, Australian pair Matt Temple and David Morgan failed to advance to the semi-finals.