Bolli's 14-under-par 270 earned him $90,000 and lifted his winnings for the season to nearly $250,000, good for sixth on the tour thanks to a pair of second-place finishes and one third.
Sheehan eagled the par-4 eighth hole, but gave it right back with a double-bogey 5 on the 11th. He made three birdies the rest of the way, but couldn't catch Bolli, who birdied two of his last three holes.
Johnson played the final round in 1-over 72. His double-bogey six on the 17th hole and a bogey on No. 13 cost the Welshman the title.
Garth Mulroy of South Africa shot a 67 to join three others in fourth place with 274. Jim McGovern (69), Jason Allred (71) and D.A. Points (74) were also at 10 under.