Friday, 10 August 2018:

MACK HORTON of Australia competes during the Men's 1500m Freestyle Final on of the Budapest 2017 FINA World Championships in Budapest, Hungary.

Mack Horton should be more careful what he wishes for.

The Olympic champion may not feature in Australia's 4x200m freestyle relay team at the Pan Pacs in Tokyo on Friday after his teammates answered his call to lift in stunning fashion.

Rio 400m champion Horton could only manage 11th fastest in the 200m heats on the opening morning of the four day meet, sensationally failing to qualify for Thursday's final along with fellow Olympic gold medallist Kyle Chalmers.

Yet Horton may have only himself to blame after demanding his teammates "step it up" ahead of Friday's 4x200m relay only a day earlier.

Horton and Chalmers (ninth fastest) were blown away by a blistering 200m heats field with Aussie young guns Alex Graham, Clyde Lewis and Jack Cartwright all posting personal best times.

Third fastest qualifier Graham - a Gold Coast Commonwealth Games 4x200m relay gold medallist - went on to finish fifth in Thursday's final behind American winner Townley Haas with Lewis seventh.

Cartwright was fourth fastest qualifier but pulled out of the 200m to be primed for Friday's 100m freestyle.

While Commonwealth 200m silver medallist Horton cut a frustrated figure after the heat, he believed it augured well for their relay team in Tokyo.

He just didn't know whether he would be in it.

Horton is still hot favourite for Friday's 400m freestyle.

"They were very fast (200m) heats but that's part of the game here, there's only two (swimmers) per nation that make the final," Horton said.

"But the relay is looking strong. I think I am fifth or sixth (fastest Australian) so I might not get a relay swim but I am really happy for those guys to go fast."

Horton clocked one minute, 46.66 seconds in the heats - 0.77 outside his personal best.

He went on to finish third in the B final.

Horton still hopes to make an impact in the 400m on Friday.

He has the second fastest 400m time of 2018 behind arch rival, China's Sun Yang who is not in Tokyo this week and is more than three seconds quicker than the next Pan Pacs threat, 11th-ranked American Zane Grothe.

But Horton admits he does not know what to expect in the 400m as he juggles his program.

Horton has ditched his beloved 1500m freestyle to concentrate on the 200m, 400m and 800m freestyle before the latter event makes its Olympic debut in 2020.

He warned it may be another 12 months before he sees results.

AAP