Roberts hit a pitching wedge to 6 feet and made birdie at the 18th hole at En-Joie Golf Club to finish at 15-under 201 and edge Funk, who also shot a 65. It was the 12th victory on the Champions Tour for the 54-year-old Roberts, who rallied from five shots behind with eight holes to play.
Local favorite Wayne Levi (69) tied for third at 13 under with Nick Price (68) and Dan Forsman (71), who bogeyed three of the final five holes to lose the lead he held for most of the day.
Mark Calcavecchia, who turned 50 two weeks ago and was bidding to win his tour debut tour, never mounted a charge and finished at 12 under and tied with Brad Bryant (71) and Bill Glasson (69).
Ken Green, who shot a 2-over 74 on Saturday as he adjusts to the game wearing a prosthetic device on his lower right leg, withdrew Sunday morning because of pain and said he would not play next week in Montreal.
It was Forsman's tournament to win, but after making just one bogey over the first two rounds he self-destructed at the end.
Forsman made a pretty 8-foot putt that broke left-to-right and into the hole for birdie at No. 11 to vault into sole possession of the lead at 15 under.
Moments later, Roberts chipped in from the rough for eagle at No. 12 to begin his late surge, and followed that with birdies on the next two holes to move into contention.
Forsman reached 16 under with a birdie putt from inside 2 feet at No. 12 that he nearly missed. He then made bogey at the par-3 14th hole, running his 25-foot putt to within 2 feet of the hole but missing the easy par putt to give Roberts new life.
"My putting has been a little bit of an issue," Forsman said. "I think that's what happened down the stretch. I just wasn't popping the putter as well."
It was the second straight bogey at 14 for Forsman, and his struggles continued at the next hole when he hit a poor drive, hit his second shot into a greenside bunker and made bogey again.
Roberts birdied No. 16 to gain the lead by a shot but returned the favor at the par-3 17th hole when he drove the rough behind the green and was unable to get up and down.
The five-shot lead Forsman had held over Roberts had vanished in a span of five holes, and when he went to the tee at 16, Forsman was in a three-way tie for the lead, with Price and Levi just a shot behind.
Funk, who started the day five shots off the lead, had four birdies on the front nine as he took advantage of the ideal scoring conditions and his third birdie on the back side, at No. 16, left him within one shot of the lead. Funk drove the green at the par-4, but left his downhill try for eagle just short, then parred the final two holes and watched Roberts win it from the scorer's tent.
Forsman began the hot, humid day with a one-shot lead over Bryant and was immediately distracted on the par-4 opening hole. Lying 8 feet from the pin after two shots, Forsman had to pull away from his birdie attempt when a yellow butterfly landed on the face of his putter. When he resumed his stance, the butterfly briefly alighted on the cup before flying away, and he missed the putt.
Forsman rallied with birdies at both par-5s on the front nine, lipped out a birdie try at No. 9, and made the turn tied with Price at 14 under.
Price, who lamented two bogeys on the back side of Saturday's second round, began the day three shots off the lead and quickly moved into contention with eagle at the 554-yard, par-5 third hole. He followed with birdies at Nos. 6 and 7 to move to the top of the leaderboard. Forsman had a chance for eagle at No. 8, but he was poor with a chip-and-roll from the fringe above the pin and had to settle for birdie.
Price's surge halted in dramatic fashion at the par-5 12th hole, statistically the easiest on the narrow the 6,974-yard course. He drove the trees lining the right side of the fairway and pulled his third shot onto a cart path, where it rolled up against a retaining wall lining a water hazard. Price nearly saved par, but hit his long putt too hard and it bounced off the edge of the cup and stayed out.
"I've got to make birdies, I need three maybe four birdies," Price said as he walked up the 13th fairway after his second shot had landed 8 feet from the pin. "I'm going to try."
Moments later, his birdie try lipped the left edge of the cup and didn't drop, and he never recovered, making par at the final six holes.