By Rod Gilmour
KAZAN, Russia (Reuters) - Mystery surrounded the conclusion of the world championships on Sunday when China's twice champion and favorite Sun Yang failed to start the men's 1,500m freestyle final won by Gregorio Paltrinieri.
As the Italian celebrated his first world title the sport's governing body FINA said a chest complaint had caused the Sun to pull out minutes before the distance race, denying him the chance to claim his third title of the week.
"I feel very sorry that I couldn’t be present for the 1500m," Sun told reporters.
"I didn’t feel good in my heart. Today I felt really uncomfortable at the pool during my warm-up and I had to give up the idea of competing. I feel really sorry about that.
"It happened after the warm-up as I was preparing for the competition. It is the first time I have felt uncomfortable in competition."
Sun was asked about reports that he had an altercation with a Brazilian swimmer during training in the adjacent pool.
"I have no comment because it was a morning problem," he said.
In the absence of Sun, who won the 400m and 800m freestyle titles not on the blocks, Paltrinieri set a European record 14 minute 39.67 seconds to claim gold.
But the Italian was nearly made to pay for his opening 800m as pursuing American Connor Jaeger finished 1.53 seconds behind with Canadian Ryan Cochrane third.
France continued its domination of the men's 50m races with Camille Lacourt retaining his 50m backstroke title in 24.23 seconds -- the fifth fastest in history as he held off American Matt Grevers and Australia's Ben Treffers.
The women's 50m breaststroke final provided two shocks as Sweden's Jennie Johansson touched for gold in 30.05 seconds with Jamaica's Alia Atkinson runner-up. Yuliya Efimova, the controversial Russian who was returning to major competition after a drugs ban, finished third.
Ruta Meilutyte, the Lithuanian favorite, had twice gone under 30 seconds ahead of the final but finished fourth with only 0.09 seconds separating the first four.
Rising Australian Bronte Campbell clocked 24.12 seconds to win the women's 50m freestyle, adding to her 100m title.
Campbell, younger sister of fourth-placed Cate, held off world and Olympic champion Ranomi Kromowidjojo of the Netherlands by 0.10 seconds with Sweden's Sarah Sjostrom third.
Japan's defending champion Daiya Seto produced a searing breaststroke leg to take command of the men's 400m individual medley final, then stayed composed on the freestyle section to win in the year's fastest time.
Hungary's Katinka Hosszu was inside world record pace at the final turn as she just held on to defend her title and complete the 200m and 400m individual medley double.
Hosszu clocked 4:30.39 over 400m -- 0.08 seconds outside her Hungarian record -- with fast-finishing Maya DiRado taking silver and Emily Overholt of Canada bronze.
The men's 4x100m medley relay saw the United States regain world bragging rights with their quartet posting 3:29.93 to leave Australia and defending champions France in their wake.
In the closing women's 4x100m medley final, fastest qualifiers China kept up their domination to secure gold.
The U.S. topped the final medal table, with 23 in total -- eight gold, 10 silver and five bronze.
Australia finished on seven golds with China and Britain locked on five each.
(Editing by Ed Osmond)