Defying the incessant rain and stop-start chases by his nearest pursuers, the 35-year-old from Georgia's deep south won the 151st edition of the sport's oldest and most distinguished tournament on Sunday by six strokes.
Having led by five shots from half-way, Harman, who was a 100-1 outsider at the start of the tournament, did a couple of times have his lead reduced to three – but showing the sort of composure of a man who spends his leisure time shooting wild pigs, deer and alligators, he responded emphatically each time a threat emerged.
He even got some help from a fan who growled at him in the rain, 'Harman, you don't have the stones for this'.
"That helped snap me back into 'I'm good enough to do this'," smiled Harman. "I'm going to do this. I'm going to go through my process, and the next shot is going to be good."
And it was. The dead-eyed left-handed marksman, whose putting was a thing of beauty all week at Hoylake, ended up shooting a final-round 70, finishing ahead of a four-way tie for second place, where Australian Jason Day shared the runner's-up spot with Korea's Tom Kim, Austria's Sepp Straka and Spain's Jon Rahm.
Queenslander Day shot a two-under 69, Kim 67, Day 69 and Rahm, seen as the big danger after his dazzling 63 on Saturday, a 70 - but their hunts were all hit-and-miss, certainly not helped by the rain that never let up all afternoon on the famous English north-western links.
"Armageddon," Harman called it, admitting he's never done well playing in the rain before.
But even though Rahm got within three strokes early on Sunday and Straka did likewise later in the round, Harman, after the same sort of nervy start he had suffered on Saturday, proved rock-solid to become only the third left-hander to win the Open, after Bob Charles (1963) and Phil Mickelson 10 years ago.
Only two players had ever had squandered a five-shot lead after 54 holes in the Open - Macdonald Smith at Prestwick in 1925 and Frenchman Jean van de Velde, famously, at Carnoustie in 1999.
But, in truth, the Ricky Ponting-lookalike Harman never really looked ready to do anything but smash his opposition for six, such was his control over the last 36 holes.
Indeed, apart from the early blips when he dropped a shot at the second and then had to take a penalty drop at the fifth as his tee shot ended in a bush, Harman's response to having his lead cut only brought the best out of him, with a birdie at the seventh his immediate response.
Straka also put the pressure on with a birdie on 16 but Harman immediately hit back by holing from 40 foot at the 14th.
There's no question that Harman joins the list of the more unlikely Open champions of late - like his compatriots Todd Hamilton in 2004 and Ben Curtis the year before - as he hadn't had a win of any sort in six years.
But the Open definitely also a bit of a one-off as its new champ, who planned to spend the evening supping Guinness from the Claret Jug.
"I'm a bow hunter. I bought a new tractor for my hunting place a couple of weeks ago, so I'll get home and I'll be on the tractor mowing grass in the next few weeks, so I'm excited about that," said Harman.
"It's on order. It's a 105-horse orange Kubota tractor and it's going to be a pretty one."
Er, celebrating an Open win by mowing 40 acres on a tractor?
"I've got a lot of layers, man," responded Harman delightfully. "I'm like an onion."
