s Kirk won the McGladrey Classic at Sea Island after a mistake by fellow overnight leader Briny Baird on the 18th hole.
A four-under 66 was enough for Kirk to claim his second PGA Tour title on a total score of 14-under overall, with Baird one stroke behind on 13 under after a final-round three-under 67.
The two Americans were tied going into their 72nd hole of the week, but Baird – still yet to win his maiden Tour title after 365 attempts – drove into a fairway bunker off the tee before hitting into a hazard as he attempted to recover.
Kirk played for par after realising Baird's mistake, and he added a second title to the Viking Classic he won in 2011.
Australian John Senden finished two strokes adrift of Kirk in equal fourth on 12 under after a three-under 67 on Sunday saw him relinquish the overnight lead.
Baird held a one-shot lead at the 15th and it looked as if he was going to seize control of the tournament after securing a 40-foot eagle chance while Kirk played into the water and then left his chip 20 feet short of the flag.
But Baird missed his eagle attempt and three-putted for par with Kirk sinking his long par putt to not lose any ground on his compatriot.
Kirk's birdie on the par-three 17th then tied him with Baird before the late drama on the 18th.
South Africa's Tim Clark made a late charge and finished tied for second with Baird after an eight-under 62 that featured six birdies in the first 10 holes.
Scott Brown and Brian Gay joined Senden in a tie for fourth on 12 under after all both enjoyed consistent weekends.
Pre-tournament fancies Matt Kuchar and Webb Simpson tied for seventh on 10 under.
Greg Chalmers was the next best Australian on eight under in equal 10th spot.