Snedeker then closed his round with an uneventful par on No. 18, while Petrovic sent his drive into the woods on the left side of the fairway and wound up finishing with a bogey.
"A guy shoots 63, you've got to take your hat off to him - he won it, I didn't lose it,'' Petrovic said.
Though he was denied his second career victory and first since 2005 when he won the Zurich Classic of New Orleans, he did stand to move up 42 spots to No. 82 in the FedEx Cup standings and ensuring himself of making the field for The Barclays this week and next week's Deutsche Bank Championship.
"At least I'm guaranteed the first two,'' Petrovic said. "I just kind of had an off year, and I saw signs of life, my game starting to get a little better.''
Snedeker was at 18 under before a late run of three consecutive birdies thrust him up the leaderboard. He capped the string with one on the par-5 15th.
His previous best finish on the tour came in January when he was third at 12-under in the Buick Invitational after shooting a career-best 61 in the first round.
Overton - the 24-year-old former Indiana player who led after the second and third rounds and entered with a three-stroke lead - played himself into the FedEx Cup. He came to Greensboro at No. 165 on the points list but picked up 1,867 points and jumped to 109th.