Summerhays fired an 8-under 64 in the final round to finish at 15-under- par 201, which was good for a one-shot win over Jim Thorpe (66), 2003 winner Gil Morgan (66) and overnight leader Doug Tewell (71).
'I'm so excited,' said Summerhays, who pocketed $225,000 for the victory. 'Sixty years old and winning golf tournaments still. I doesn't get any better than that.'
Summerhays broke out of a tie for first with a spectacular shot at the par-5 closing hole at the TPC at River's Bend. He came up short with his second shot, but hit a wonderful bump-and-run shot that stopped two feet from the cup. Summerhays tapped in to reach 15 under par, but had to wait to see if any of his closest competitors could catch him.
Thorpe was the first to give it a go. He held the lead until a bad bunker shot at the 16th cost him a stroke. Thorpe's blast out of the sand came up 12 feet short and he missed the putt to fall two behind Summerhays.
Thorpe, one of the longest hitters on the Champions Tour, reached the green in two at No. 18 and gave himself a reasonable a chance at eagle. His eagle putt from 20 feet missed left and Thorpe converted the birdie putt to get to minus-14.
Morgan was next up to challenge Summerhays' lead. The defending champion birdied the 10th and 11th to get into the mix, but it was a 7-footer for birdie at the 14th that tied him for the lead at 14 under par.
Once Summerhays took first, Morgan needed a birdie on the way in to try and repeat. Morgan also found the 18th green with his second shot, but three-putted for par to share second.
Tewell, the overnight leader by one after Saturday's second round, took sole possession of the lead before Summerhays reached 15 under par. Tewell, who battled a left elbow injury throughout the final two rounds, ran home a 6-footer for birdie at the 15th, but found trouble at the next hole.
At the par-3 16th, Tewell hit a 4-iron into the bunker short and right of the hole. He failed to save par to fall one down and missed a 15-footer for birdie at the 17th.
Tewell was in almost the same position Summerhays was in a few groups earlier. Tewell's second came up short and left, but unlike Summerhays, his chip checked up and stopped 35 feet from the hole.
Tewell missed the putt and Summerhays collected his third title on the Champions Tour. It was also his first since the 1998 State Farm Senior Classic.
'I had a few people not make birdie on that last hole and that's unfortunate for them,' said Summerhays. 'It was a good day for me. It was fun. The chip on the last hole was beautiful. It's nice to be under the pressure and chip one up there where you could miss it, but it would be difficult.'
Summerhays trailed by six at the start of Sunday's final round. He tallied four birdies and a bogey in a six-hole span on the front nine, but his play at the start of the second nine sent him to the winner's circle.
He birdied the 10th and ran off four in a row, including a 3-footer at the 13th that tied him for the lead at 14 under par. Summerhays' birdie at the last polished off a back-nine 31.
Mike Reid shot a 5-under 67 on Sunday to share fifth place with Des Smyth, who only managed an even-par 72. They came in knotted at 12-under-par 204.
David Eger (68), Fred Gibson (70) and Hale Irwin (69) tied for seventh at minus-11.