On a dramatic final day of wildly fluctuating fortunes for those at the sharp end of affairs, Coles pipped local hero Paul Lawrie to the £93,000 first prize by a single shot after the 1999 Open champion suffered a calamitous stumble over the line.
Coles, four-strokes off the lead overnight, seized his opportunity and added the PGA Seniors crown to the Senior PGA Professional Championship title he won back in May.
Standing on the 16th tee, PGA Honorary member Lawrie was two-shots clear and on course for a fourth victory on the Legends Tour.
But a brace of bogeys at 16 and 17 saw his lead evaporate and a ruinous double-bogey on the 18th opened the door for Coles, who could even afford the luxury of a bogey on his closing hole.
The PGA stalwart’s one-under 71 – the only sub-par card in the top-10 – gave him a four-under aggregate while Lawrie’s 76 left him on three-under.
During Saturday’s third round, Coles trudged to the turn in 41 shots but he dug in coming home with a couple of late birdies to keep himself in the mix. His spirited effort there was rewarded with the ultimate prize on a super Sunday.
The 51-year-old, who received a congratulatory phone call from former US President Donald Trump, added: “After nine holes on Saturday, all I was thinking was that I’d have an earlier tee-time on Sunday and I might be home a bit earlier.
“But again, patience has been key. I knew if I could string a few pars together after that outward half it would stop the bleeding. As long as I stayed in red figures I’d be OK. And I was.”
A week ago, Coles gave himself a timely lift with a spirited back-nine on the final day of the Senior Open at Carnoustie to finish just inside the top-30.
“I was four-under for that nine and it actually gave me a bit of momentum coming into this week,” he said. “If it wasn’t for that I would have maybe been struggling.
“It gave me a bit of a jump-start coming here. I was confident but I never expected to win.”
With Lawrie slipping back into second, another PGA Member, Simon Khan, claimed third on one-under after a 74. Only the leading trio finished under-par.
Tournament host Colin Montgomerie managed a share of seventh on two-over after a third 73 in a row.
Click here for the final round scores.