The tournament came down to the wire as Duke and Kevin Stadler were knotted at 12-under par, with Daley one stroke back when Duke stepped to the par-5 17th tee.
Duke, who was 3 under thanks to four birdies and one bogey on Sunday, found the fairway off the tee at 17 at the Cliffs Valley course at The Cliffs Golf & Country Club, which along with the The Cliffs at Keowee Vineyards and The Cliffs at Walnut Cove hosted the first three rounds. His approach did not reach the green, but he chipped to 2 feet. Duke converted the birdie try to move to minus-13.
Both Daley and Stadler had cracks at the 17th and Daley was the only one to take advantage. His second missed the green right, but he pitched to four feet and drained the birdie putt to get within one.
Stadler found the short grass with his tee ball, but had a horrible angle to go at the flag. He laid up, then hit a bad approach that spun back to 35 feet. Stadler, who won earlier this season on the European Tour, did not hole the putt, and trailed Duke by one with one to play.
At the closing hole, Duke hit a strong 3-wood into the fairway, but made a horrible mistake with his approach. Holding a 9-iron, Duke pulled it left against a grandstand.
'It's just a bad shot,' acknowledged Duke, who collected $112,500 for the win. 'The wind picked up and I dropped my head and took it to the left.'
He took his free drop, but had little green to work with and a mound in front of him. Duke pitched into the hill and watched the ball roll 4 feet short of the stick. He made the clutch par save to get into the clubhouse at minus-13.
Daley and Stadler were in the fairway at 18, but Stadler did not give himself a great look at birdie. He missed his long try, meaning Daley, who hit a 9-iron 15 feet left of the target, was the only one who could catch Duke.
Daley's putt never threatened the hole, giving Duke the title.
'You have to take one day at a time and try and make as many putts as you can,' said Duke, who moved to fifth on the Nationwide Tour money list. 'I hit it great all four days.'
Daley managed a 3-under 69, while Stadler actually missed his par putt at 18. He shot a two-under 70 and shared third place with Grant Waite, who fired a 5-under 67 on Sunday. The pair came in at 11-under-par 275.
Overnight leader Richard Johnson never got anything going on Sunday. He shot an even-par 72 and tied for fifth place with 2000 U.S. Amateur champion Jeff Quinney (68), Johnson Wagner (68) and Chris Stroud (71). The group came in at minus-10.
Steve Collins (69), Bob Heintz (69), Doug LaBelle II (69) and Scott Weatherly (71) tied for ninth place at 9-under-par 277.