The 42-year-old Johnson, also a playoff winner two weeks ago in the Rex Hospital Open in Raleigh, N.C., has six Nationwide Tour victories, matching the record shared by Sean Murphy, Matt Gogel and Jason Gore. With two victories this season, Johnson is a win away from earning an immediate promotion to the PGA Tour.
Johnson closed with a 4-under 68 to match Iles at 20-under 268 on the Fox Den Country Club course. Isles tied the course record with a 63.
Johnson earned $94,500 to jump from third to second on the money list with $253,445, with the final top 25 earning 2010 PGA Tour cards.
Johnson ended the playoff with a short birdie putt on the par-5 18th.
It was maybe only a foot but it sure looked longer than that because of what it was worth, the former Clemson player said.
Blake Adams (65) and David McKenzie (72) tied for third at 19 under, and Tjaart van der Walt (66) and Jason Schultz (66) were another stroke back. McKenzie, three strokes ahead of Johnson after the third round, three-putted the 18th for a bogey.
The end of regulation was basically a playoff, too, Johnson said. If one of us makes birdie there we dont need the playoff. I figured at worst, you make a par and youre in a playoff.
Johnson and Isles opened the playoff with birdies on 18, with Johnson rolling in an 8-footer and Iles following with a 6-footer to send it back to the 18th tee. Iles then left his wedge 10 feet shy of the pin, while Johnson spun a wedge back from 90 yards to 15 inches to set up his winning birdie.
The last two years were just dismal, said Johnson, who made only three of 22 cuts in 2008 and three of 14 the year before. Its not like I was playing poorly, I just couldnt get off the cut line. I knew I needed to do something because what I had wasnt working. I needed to make a change or quit playing.
Johnson sought out Jeff Leishman, an acquaintance of a dozen years and a coach to several of Johnsons cohorts.
I think I went searching for a new golf swing and a new Kevin Johnson, he said. Jeff didnt make big changes but worked on getting me back to what makes me tick. I had gotten to steering it around with handcuffs on. It wasnt fun playing.
Australias Michael Sim, also a two-time winner this year and the money leader with $388,117, missed the cut.