The high-school student clocked two minutes 07.01 seconds, breaking the previous world mark of 2:07.28 set by Daniel Gyurta of Hungary on August 1 at the London Olympics.
“To tell the truth, I targeted to clock 2:06:00s,” Yamaguchi said after his record-breaking swim in Gifu, central Japan, adding that he was eager to show off his talent on the world stage.
“I’m really looking forward to the world championships next year. I want to be a swimmer who can succeed (Kosuke) Kitajima, whom I admire a lot,” he added.
Yamaguchi failed to qualify for the Olympic 100m and 200m races after he finished third over both distances in the national championships, which were won by two-time double Olympic gold medallist Kitajima.
However, Kitajima, 29, did not win a medal in the 100m and 200m breaststroke in London.
Yamaguchi came close to Gyurta’s 200m world mark when he swam 2:07.84 at a national high-school meet on August 17.
“Since I started working under the wing of coach Norimasa Hirai, I became stronger mentally and my body became bigger. I think I can compete against the world in the 200 metres. I also want to compete in the 100 metres,” he said.