Kosuke Kitajima shattered the men's 200 metres breaststroke world record on Sunday, the Japanese double Olympic gold medallist clocking two minutes, 7.51 seconds to slice almost a second off the existing mark.
The 25-year-old's time eclipsed American Brendan Hansen's two-year-old record of 2:08.50 at an Olympic send-off competition in Tokyo ahead of August's Beijing Games.
"I feel like crying," Kitajima told reporters.
"It was a perfect swim and has given my confidence a real lift. Of course, I'm only thinking about winning gold in Beijing and if I don't win gold I won't come back."
Kitajima won gold in the 100 and 200 metres at the Athens Olympics four years ago but has largely played second fiddle to rival Hansen since. Hansen still owns the 100m mark.
"It's great at this stage to break one of Hansen's records," said Kitajima after setting a world best for the first time since 2003.
"I kept getting beaten by him (Hansen). Now I can go to the Olympics aiming for the gold medal."
Kitajima, who is contracted to Japanese manufacturer Mizuno, broke the world record wearing one of Speedo's controversial LZR swimsuits.
World records have tumbled over the last few months, almost all by swimmers wearing the LZR suits, which the British company says reduces drag, muscle oscillation and skin vibration.
Japanese officials have yet to announce whether they will allow the country's swimmers to break contract and wear Speedo suits in Beijing.
However, Kitajima has demanded the swimmers be allowed to choose what swimwear to use and given the right to ditch approved makers Mizuno, Descente and Asics in favour of Speedo.