Wales outclassed Japan 53-30 in the second test in front of 23,000 spectators at the Prince Chichibu Memorial Rugby Stadium in Tokyo on Sunday.
Japan, however, put in a much improved performance from last week's thrashing in the first test and actually led Wales 20-19 at half time.
Wales stepped up a gear in the second half, scoring three quick tries in a five-minute spell that knocked the stuffing out of Japan. Although they fought gamely to the end, the Japanese were never able to get back into the game.