Piercy, a 29-year old Las Vegas resident, posted his 13-under-par 267 total and then waited an hour to see if anyone could catch him.
Nobody did and the former San Diego State standout pocketed $94,500, pushing him from No. 35 to No. 12 on the money list and locking up a spot on the PGA TOUR next season.
Cameron Percy (66) and Brendon de Jonge (68), last weeks winner, tied for second place, two shots back. Jeff Gallagher (66), Rich Barcelo (68) and Canadian Brad Fritsch (67) tied for fourth, three behind.
Piercy becomes the Nationwide Tours third multiple winner in 2008, joining Australian Jarrod Lyle and 2007 U.S. Amateur champion Colt Knost.
Its been amazing, said Piercy, who won the Preferred Health Systems Wichita Open two weeks ago and finished tied for sixth at last weeks Xerox Classic. I felt its been coming, even when I was 123 on the money list. I tweaked a couple of things, which is mainly taking the bogeys out. The last three weeks Ive been taking the bogeys out of play.
Piercy didnt seem to have much chance Sunday. He bogeyed the par-3 ninth to make the turn at Elmhurst Country Club at even-par, and four strokes back of the leaders.
Piercy sneaked up the leaderboard, starting with a 15-foot eagle putt at the par-5 11th. He then added four birdies in the next five holes, including a 40-footer at No. 15.