[5] Sone was surprisingly eliminated in the second round of the 1960 All-Japan Judo Championships, a contemporary report by the martial artist Donn F. Draeger calling his performance there a "pitiful sight" and mentioning that he was aging.

[6] Sone won a silver medal at the 1961 World Judo Championships in Paris, behind Anton Geesink.

[7][8] His loss against Geesink, 5th dan,[9] was heralded as the end of the era in which the best Japanese judokas could not be defeated by foreigners.

Within nine minutes of the 20-minute contest, a foot sweep forced Sone onto the ground where he was held for the necessary 30 seconds with a Mune-gatame.

But the Japanese team hoped to beat him with Isao Inokuma in the all-weight class the next day.