Sunday, 30 July 2017: Mack Horton of Australia and Italy's Greg Paltrinieri will put friendship aside in the 1500m freestyle final at the world swimming championships at Budapest.

With friends like Italy's Greg Paltrinieri, Mack Horton doesn't need enemies as he targets 1500m freestyle glory.

Olympic 400m champion Horton looked to have dodged a bullet when his Rio nemesis Sun Yang of China pulled out of the 1500m event at the world swimming championships at Budapest citing fatigue.

Yet there will be no let up for the 21-year-old Australian in the final at Duna Arena on Sunday (Monday AEST) thanks to one of his close mates, Olympic and defending world champion Paltrinieri.

The pair struck up a friendship while training together in Melbourne, so much so that they went on holiday together with their partners after the Rio Olympics.

But there were will be no love lost when Paltrinieri lines up against Horton in the premier distance event Australia once owned.

"I love Mack but I want to beat him," Paltrinieri said. "I will look at him sometimes during the race because he is dangerous."

Expectations are high for Horton in the 1500m after he ditched the 800m freestyle from his world titles program to concentrate on it.

He is aiming to become Australia's first 1500m world champion since his childhood idol Grant Hackett claimed his fourth crown in 2005.

Overall Australia have won six 1500m world titles, including five straight from 1998.

However, Paltrinieri sounded his intentions when he set a blistering 1500 heats pace with top qualifier Mykhailo Romanchuk of the Ukraine.

Romanchuk touched out Paltrinieri in qualifying, more than 15 seconds faster than Horton's heat.

Horton at one stage looked like he may not even qualify for the final but scraped in as seventh fastest by 0.02 of a second.

Horton hinted that the likes of Paltrinieri may have peaked too early.

"They are wasting a lot of energy right now," Horton said of Paltrinieri's scorching heats duel with Romanchuk.

Horton made no apologies for cruising through his heat, having faded to fifth in the Rio 1500m final - his one regret from a 2016 Olympics highlighted by his 400m win over Sun.

"I thought that's what caught me up in Rio. I just didn't have that energy at the back end of the week - I was pretty cooked (in Brazil)," Horton said.