Jason Day has imploded during the third round of the US PGA Championship to give away a solid chance at a second career major.
After starting day three of the year's final major just two shots off the pace, the Australian world No.7 crashed out of contention spectacularly with a six-over-par 77 at Quail Hollow in North Carolina.
Day, who won the 2015 US PGA Championship, plummeted to a share of 16th at even par, seven shots back from leader Kevin Kisner.
The American Kisner also battled to a rollercoaster 72 but at seven under the card the South Carolina native clung to a one-shot lead over world No.3 Hideki Matsuyama (73) and Chris Stroud (71).
Justin Thomas (69) and 2010 British Open winner Louis Oosthuizen (71) share fourth a shot back at five-under.
Playing in Saturday's final group with Kisner and Matsuyama, Day's nightmare round was epitomised by a bizarre decision on the par-4 18th hole to go for the green with his approach after finding trouble from the tee.
The 29-year-old Australian hit his second shot into a shrub and had to take a penalty drop en route to a crippling quadruple-bogey 8.
It soured a brief comeback during which Day bagged three consecutive birdies from the par-4 14th which kept him in the hunt despite a poor opening 13 holes.
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Day gave back a shot on the front nine at Quail Hollow before a nightmare two holes saw the Queenslander double-bogey the par-4 12th and bogey the par-3 13th.
Fellow Australians Adam Scott and Marc Leishman are well off the pace after three rounds.
Leishman carded a 71 to remain at four-over while world No.17 Scott fell further back of the lead with a 74 to sink to eight-over for the championship.