China's Sun Yang swims in the men's 800m freestyle final at the World Swimming Championships in Gwangju he finished 6th. Photo: Mark Schiefelbein/AP Photo

GWANGJU  Italy's Gregorio Paltrinieri swam a dominant European record to win the 800-metre freestyle at the world championships in South Korea on Wednesday and leave the controversial Chinese Sun Yang a distant sixth.

The 24-year-old Paltrinieri, world and Olympic champion over 1,500m, took his first gold at the medium distance in 7 minutes 39.27 seconds with Norway's Henrik Christiansen just over 2 seconds behind. France's David Aubry claimed bronze a further 8 tenths adrift.

There was immediately more joy for Italy as veteran Federica Pellegrini successfully defended her 200m freestyle crown against Australian teenager Ariarne Titmus and Sweden's Sarah Sjostrom.

Hungary's 19-year-old Kristof Milak not only claimed the 200m butterfly gold but did so in a world record 1:50.73, erasing one of best marks held by American great Michael Phelps.

Britain's Adam Peaty completed one of the most expected doubles of the championship by retaining the 50m breaststroke to go with his 100m honour.

And Peaty towelled down only briefly before helping Britain to bronze in the 4x100m mixed medley relay behind the United States and Australia, who won on the touch thanks to Cate Campbell.

Sun had been going for a third gold in Gwangju after claiming the 200m and 400m frees but was at the back of the pack throughout and eventually finished 5.74 seconds off the winner.

Duncan Scott of Britain and Mack Horton of Australia had protested Sun's participation at the event by refusing to shake hands, be pictured with him or take to the podium beside him during their medal ceremonies in those events.

Sun, a multiple world and Olympic champion, served a secret three-month doping ban in 2014 and is currently competing despite a case at the Court of Arbitration for Sport (CAS) over doping test samples being smashed in a confrontation with officials last year.

The 27-year-old Sun received a warning from swimming governing body FINA but the World Anti-Doping Agency wants the case heard at the CAS, which won't happen until after the worlds.

Pellegrini, 30, claimed her sixth worlds gold overall and fourth in the 200m free in 1:54.22 minutes, pulling away from Titmus in the last metres to win by 0.44 seconds. Katie Ledecky, who Titmus had shocked in the 400m free, had previously scratched with illness.

Butterfly specialist Sjostrom meanwhile added a bronze to her collection after being beaten by another teenager, Canada's Maggie MacNeil, in the 100m fly.

In the men's 200m fly, Milak proved the potential he showed in taking 100m fly silver at the home worlds in Budapest two years ago. He reduced Phelps' 2009 world record - aided by a now banned polyurethane suit - by 0.78 seconds to leave Daiya Seto over 3 seconds behind in silver.

"It's a tremendous honour to beat such a great man's world record," Milak was quoted by the Olympic Channel.

"When I turned back and I saw the time, 1;50.73? All the pressure and tension just went off my back and all the joy came out."

Defending champion Chad le Clos of South Africa faded to third in a distant 1:54.15 minutes having led the race out at world record pace for the first half.

Peaty, who broke the elusive 57-second barrier for 100m earlier in the meet, was untouchable over the sprint to win in 26.06 seconds, slightly outside his own world record.

The Brazilian pair Felipe Lima and Joao Gomes Junior were delighted to take the minor medals around 6 tenths back.

In the mixed medley relay, Russia led early before the US fought back to lead into the final freestyle leg swam by Olympic 100m champion Simone Manuel. A win would have kept alive Calaeb Dressel's hopes of a perfect eight golds at the meet.

Campbell, world 100m champion in 2013 and part of the victorious women's 4x100m relay team in Gwangju, was not to be denied though and eventually touched the wall just 2 hundredths in front.

Britain pipped Russia for bronze to give Peaty a second medal on the night and third of the championships.