Kosuke Hagino outshined two-time double Olympic champion Kosuke Kitajima on the first day of the Japanese national swimming championships on Thursday.
The 18-year-old Hagino, who clocked a new national record of four minutes 08.94 seconds to win the bronze medal at the London Olympics, improved his time to 4:07.61 to win the men's 400-metre individual medley.
Daiya Seto finished second in 4:12.70 to qualify with Hagino for the world championships in Barcelona starting on July 19.
"I was a bit disappointed, because my target was to cut 07.00, but I firmly improved my personal best, so I think the time paved my way towards the world championships," said Hagino, winning the title for a second year running.
Kitajima, the 100m/200m gold medallist in Athens and Beijing, edged past world 200m record holder Akihiro Yamaguchi by only three hundredths of a second to win the men's 100m breaststroke in 1:00.78 for his third straight and 12th overall title.
"I hadn't expected to win with this time, so I was surprised, I started training late and I need more time to get back to my top form," said Kitajima.
Yamaguchi said: "To win the national title is one of my dreams. It was so close, only three hundredths of a second. I really want to race it again."
Both Kitajima and Yamaguchi missed the bottom line for qualifying for Barcelona.
In other races, London Olympic bronze medallist Satomi Suzuki won the women's 100m breaststroke in 1:07.43 for a fourth year running, while Chihiro Igarashi defeated defending champion Asami Chida to win the 400m freestyle.
Yuka Kato won the women's 50m butterfly in 26.47 for her sixth time, Ryo Takayasu took the men's 50m butterfly in 24.00 for his eighth time, and Shinri Shioura won the men's 100m freestyle in 48.78 for his first national title.