Eighteen holes sit between Dan Brown and one of the greatest sporting upsets of our time.

Before a ball was struck at Royal Troon, little was known by anyone outside golf’s anorak contingent about this 750-1 outsider. No wonder; Brown arrived in Ayrshire as the 272nd ranked player in the world. His last eight results include one withdrawal, six missed cuts and a tie for 61st. How was anybody to know this bearded, fag-smoking, son of a Yorkshire pig farmer could come within one Open round of bringing home the bacon? There are shades of Todd Hamilton, who won at Troon in 2004. Hamilton had, unlike Brown, at least competed in a handful of majors before he landed at the oldest of them all. Brown should be completely ill at ease with this environment. Instead, he has taken to it like a pig in …

As Rory McIlroy, Tiger Woods, Bryson DeChambeau, Ludvig Åberg and Tommy Fleetwood exited after 36 holes, Brown continued to pen the archetypal underdog story. His smooth, rhythmic swing held firm over a brutal closing stretch until the final hole, when a tugged iron shot into sand triggered a double bogey. Advantage Billy Horschel, by one at four under par.

Brown’s 65 to begin this tournament was treated with disdain in certain quarters (including perhaps this one). Received wisdom was that the 29-year-old would quickly slide back towards oblivion as marquee names jousted for the Claret Jug. The slums of Chicago are full of individuals who have led major championships after 18 holes. By the turn on day three, Brown was back atop the leaderboard. At this point – in weather Mr Brown Snr would not put his animals out in – he had Shane Lowry and a rampaging Horschel for company. History favours the likes of Horschel and Brown; five of the previous six Troon Opens have been claimed by players who were without a major until that point. Horschel, a Floridian, rather astonishingly donned shirt sleeves for one of the bleakest days of summer. Round three was all about mental fortitude. At its conclusion, because of that late aberration, Brown was among a sextet at three under.

There were dramatic moments in the midst of downpours. Brown’s errant tee shot at the 7th almost took out the world No 1, Scottie Scheffler, who was a hole ahead. The Yorkshireman steadied himself to make a birdie. Brown and Lowry both found a greenside bunker at the Postage Stamp. Lowry, whose lead had been three after just one hole, slipped to a double bogey. Brown’s four meant he was tied at the top. Lowry never properly recovered, playing his last 11 holes in seven over. This was a ragged 77, meaning Lowry is three shy of Horschel.

Lowry had been the recipient of a huge break at the 11th after his pulled second shot cracked a member of the public on the leg and bounced into a favourable position. Without that, the 2019 champion’s ball was bound for a gorse bush. Lowry was still unable to save his par. The three-way tie had been maintained. Within an hour, the score to catch had slipped from eight under par to minus five. Brown made it six with a blissfully straightforward birdie at the 12th. Lowry erred again there, meaning Horschel was the man closest to the leader. Horschel made bogey at the 18th to slip to four under but his 69 was still sufficient to grab the 54-hole lead after Brown shipped three shots in his two closing holes.

A decade ago, Brown tweeted that he “could quite happily quit golf tomorrow”. He was reportedly applying to supermarkets for a job around the same time. And here he was, withstanding the elements and some of the finest golfers on the planet. Talk about making a silk purse out of a sow’s ear. The galleries here, so appreciative of what Brown is producing, have their unlikely hero. Notably Brown’s solo win on the DP World Tour, by five shots in Northern Ireland last year, came in miserable conditions.

Before awful weather hit after lunch, Justin Thomas had reached two under. Thomas proceeded to drop two shots over the closing six holes but he is hardly without hope for Sunday. “It’s a crazy sport and a lot of things can happen in a lot of conditions,” said Thomas, whose second round was of 78 shots. “But that’s what I signed up for, I guess.”

Thriston Lawrence, Sam Burns and Russell Henley benefited to an even greater extent from a morning tee time. The trio were three under and firmly in the mix even before so many golfers came back towards them. Justin Rose later punched the air after saving par at the last to equal that total with a battling 73. Xander Schauffele’s 69 means the US PGA champion is also minus three. Scheffler is a shot further back after a 71. At plus two, Jon Rahm and Collin Morikawa are far from out of this championship. Kim Si-woo is out of contention but celebrated a hole-in-one on the 17th. All eyes, though, remain on Brown. Can he maintain his fairytale challenge? Pigs might fly.