Shigenori Ohmori was the new Japanese 400 m hurdles champion in 1981, but Nagao overhauled his national rival at the 1979 Asian Athletics Championships, running 50.32 seconds to top the podium in a championship record time. Ohmori and Yoshimatsu rounded out the podium to make it a Japanese medal sweep at the championships in Tokyo. Nagao was the first Japanese male athlete to win the championship title. Replacing Kadhum as the region's top hurdler, he was chosen for both the 400 m hurdles and the 4 × 400 m relay team for Asia at the 1981 IAAF World Cup.