Xu's record regret

Meanwhile, China's Xu Jiayu won the men's 100m backstroke, but confessed he was "disappointed" not to set a new world record.

The 21-year-old Olympic silver medalist clocked 52.44sec. American Matt Grevers earned silver, 0.04sec back, with his compatriot and Olympic champion Ryan Murphy taking bronze at 0.15.

"My main aim is to break the world record," said Xu, who fell short of Murphy's record of 51.85sec set at the Rio Olympics last year.

"I'm a little disappointed not to break it, but of course I'm happy with the win.

"Sometimes it comes down to many factors - luck or a good swim. It can be hard to say which is the greater factor.

"The silver medalist chased me really hard, it really depended on a small pinch of good luck.

"It's quite an education, last year in Rio, a silver - this year, a gold."

Having failed to qualify for the final at the 2013 world championships, Xu's star has risen in recent years.

"I got better results in 2015; each time I compete the goal is different," he said.

"I think of a new goal to achieve every time, today it was the gold medal. Further on I will work on new goals." Grevers, 32, was delighted with his silver at his fifth world championships.

"I feel great. Even a month ago if somebody said I took the silver, I would be OK with it, but now I am here," he said. "This inspires me to get back to my best.

"Xu swam really well, I knew he was gonna go fast, he was between Ryan and I and he did it."

But Murphy, the Olympic champion in both the 100m and 200m backstroke, was far from pleased to have been beaten into third.

"I am not really happy with the result. It is not so great if you start off really well and finish in third place," said the 22-year-old.

Agence France-Presse