Russia's Evgeny Rylov admitted he was physically spent after winning the men's 200m backstroke title at the world championships on Friday.
Rylov clocked one minute, 53.61 seconds to take gold with Olympic champion Ryan Murphy of the United States second at 0.60 and compatriot Jacob Pebley taking bronze at 1.45 back.
Having taken bronze in the event at both the Rio de Janeiro Olympics and the last world championships in Kazan two years ago, Rylov said winning gold had taken a physical toll.
"To tell you the truth, I think I'm just going to fall down," said Rylov, 20, when asked if it was a dream come true.
"But this is what I've been training for, so yes, I did imagine that I would beat them all.
"That was my goal - my strategy was to give it all.
"Now I'm exhausted, but my opponents were just as tired as I was."
Murphy paid his dues to the new world champion and the American said he will have to train hard just to match him.
"Of everyone in that race, he probably had the most potential," said Murphy, the 100m and 200m Olympic champion in Rio.
"I wasn't surprised to see him and that time, that's pretty close to what he went last summer.
"He's still pretty young, he's just going to keep getting better year after year, I have to keep progressing at a rate to stay with him.
"I'm definitely disappointed, I'm a competitor I want to be the guy that's finishing first.
"That has the best time in the world, so yes, it definitely stings."