Coming into the penultimate hole only five strokes adrift of leader Jason Day, the Scot hit three balls into the water surrounding the island green before ending up with a six-over he described as an “epic fail”.
The nightmarish nine was compounded by a three-putt bogey at the closing hole and Knox ended with an eight-over 80 to drop into a tie for 40th, 13 shots behind Day at the end of the third round.
Knox's tee shot on the 17th, which played 129 yards with the pin near the front-left, was short.
Instead of going to the drop area, the Scot shanked a second off the tee well right and his third attempt also came up short.
“It's such an easy shot when you have no nerves or adrenaline,” the 30-year-old said.
“A pro would never miss that. We should know what we're doing. But it's a different story once you've hit two in a row in the water. The green felt like it was the size of a quarter.”
After pitching from the drop zone to 38 feet behind the hole, the crowd gave Knox an ironic cheer and he raised his arms in mock celebration. He holed his second putt from seven feet.
“I ended up making an awesome putt for nine,” he said.
“After I was walking through the tunnel (to 18), I was like, whoa, that was to avoid a 10.”
Only Bob Tway, who recorded a 12 in 2005, Robert Gamez (11, 1990) and Phil Blackmar (10, 1990), have scored higher on the 17th.
It was far from the only disaster on a day when only six of the field broke par.
World number one Day described the course as “nearly unplayable” after taking a pair of double-bogeys on the front nine of his third round before finishing with a one-over 73 and a four-stroke lead.
Spaniard Sergio Garcia six-putted the fifth hole, while Rory McIlroy suffered five three-putts in his 75.
“A few pin positions were on crowns and you dribble a putt by, all of a sudden it's six feet by,” the Northern Irishman said.
“There were a few pins out there that I felt were just a little too much on the edge.”
Original source: Knox rues coming up short