Sheehan, who went into the final round with a one-stroke lead over Japan's Shingo Katayama, captured his third career victory on the Japanese tour, finishing at 7-under 277.
'It's great to win such a prestigious tournament,' said Sheehan, who earned a five-year exemption on the Japanese tour as well as the $336,000 winner's prize. 'There was a lot of pressure today and the course's setup was pretty tough.'
Japan's Azuma Yano finished second after closing with a 71 for a 280 total. Katayama bogeyed three of the first four holes and finished in a five-way tie for fifth at 282.
Sheehan has also won the Fujisankei Classic and the Nippon Series JT Cup both in 2004.