Vance Veazey, who captured the season-opening BellSouth Panama Championship, posted a 71 to join Danny Ellis at 13-under-par 275 in a tie for third. Richard S. Johnson was one-shot further back at 12-under-par 276.
'Wow, what a feeling,' said Hietala, who resides in Lafayette, Louisiana. 'I can't put into words what this win means to me.'
Hietala had a one-shot lead over Johnson heading into the final round at Le Triomphe Golf & Country Club but he soon felt the pressure of O'Hair, who birdied each of his first three holes.
Hietala tallied a pair of birdies over his first four holes but dropped a shot with a bogey at the par-3 sixth to make the turn at 15 under.
The 31-year-old regained his composure on the inward half with a birdie at the par-four 10th, however, and added back-to-back birdies starting at the par- five 12th to secure a one-shot victory.
'People always say it hasn't sunk in yet or it may take two weeks for it to sink in, but I'm pretty sure mine sunk in when I tapped in on the last hole,' said Hietala, who pocketed $90,000 for the win. 'The tap-in was the most special putt ever for me especially considering the adrenaline I felt. The last three holes was the most pressure I've ever felt but that made it even more special.'
O'Hair used a 67 on Saturday that featured an ace at the sixth to get within four of the lead. He vaulted out of the gate on Sunday with three straight birdies from the first and ran off six straight pars to stand at 13 under around the turn.
The 22-year-old made a move on the back nine with a birdie at the par-3 11th and back-to-back birdies from the 14th. O'Hair then birdied the par-4 18th to cap off a round of 65.
'Today was a lot of fun,' said O'Hair, a rookie on the PGA Tour this season. 'Ryan kind of egged me on and I hope I pushed him some. I was comfortable playing out here this week and that was the key. It is the best week of my golf career so far.'
Ken Duke shot a 5-under 67 to finish seven shots off the pace at 11-under-par 277. Brandt Snedeker and Kris Cox were one shot further back at 10-under-par 278.
Brett Wetterich, Troy Matteson and Charley Hoffman tied for ninth place at 9-under-par 279.