Gay ended up at 20-under 264, collecting $1.02 million.
"It feels great," Gay said. "Just a phenomenal day. Virtually mistake-free all week."
Gay's title was his second on the PGA Tour.
Luke Donald (66) and Briny Baird (68) tied for second place at 10-under 274. Todd Hamilton (70) and Lee Janzen tied for fourth at 275 and Jose Maria Olazabal (67) and Tim Wilkinson (73) shared sixth at 276.
Rory Sabbatini (66), Matt Weibring (68) and Tim Petrovic (70) tied for eighth place, another stroke back.
Gay led by three shots after three rounds and doubled the lead with a birdie on the first hole and an eagle on the second of the final round.
"Didn't see a leaderboard all day," Gay said. "I told myself the whole time I didn't want to watch the board, I just wanted to stay focused. I kept looking down and moving ahead."