Jordan Spieth remains on course for another wire-to-wire win at the Masters, but a dramatic late wobble on Saturday saw his lead reduced from four shots to just one heading into the final round.
Spieth held a four-stroke advantage after 54 holes on his way to victory at Augusta last year and looked set to secure the same cushion this time around when birdies at the 12th, 14th and 15th lifted him clear of the chasing pack.
However, there was a sting in the tale for the 22-year-old Texan as he leaked his last two tee shots right and finished bogey, double bogey to complete a 73 - leaving him just one clear of Smylie Kaufman (69) at three under.
Perhaps more significantly, Spieth's surprising stumble brought the likes of world number one Jason Day firmly back into contention at even par, while even Rory McIlroy - who slumped to a birdie-free 77 in the company of the reigning champion - will begin Sunday only five adrift.
Two players with contrasting levels of Augusta experience, Masters rookie Kaufman and 58-year-old two-time champion Bernhard Langer, proved the somewhat unlikely stars of Saturday as they moved up to second and tied-third respectively with rounds of 69 and 70.
Kaufman's score ultimately left him just one off the pace following Spieth's struggles on 17 and 18, while Langer was joined by Hideki Matsuyama (72) at one under, with Day (71), Dustin Johnson (72) and Danny Willett (72) a stroke further back.
Spieth, looking to become only the fourth player after Jack Nicklaus, Nick Faldo and Tiger Woods to retain the Masters, battled his way to the turn in 35 strokes with typically strong work around the greens, before recovering superbly from a double bogey at 11 with a flurry of birdies.
However, more trouble lay ahead for the leader, who nevertheless set a new outright record, previously shared with the legendary Arnold Palmer, by ending a seventh successive Masters round at the top of the leaderboard.
Holes 10 to 12 at Augusta have caused McIlroy no end of problems over the years and that stretch severely dented the Northern Irishman's latest challenge as he lost further ground following a frustrating outward nine.
Day, meanwhile, will now feel he is right in the mix, despite being out-scored by his veteran playing partner in round three - the canny Langer using all his experience and know-how to move into contention 31 years on from his first Masters triumph.
While Day claimed back-to-back birdies from the 13th, the latter courtesy of a stunning 69-foot putt, Langer matched the Australian - chipping in at 14 - and then went one better by picking up another shot at the next to get to two under for the tournament.
After Day had dropped a stroke at 16, Langer ended his admirable round on a low note with a bogey at the last, but was still able to sign for the best score since Thursday's opening round.
It was not long before Kaufman topped Langer's 70 with a 69 - three birdies in the space of four holes on the back nine enough to propel the 24-year-old American into Sunday's final group.
Johnson could also have ended the day in red figures, but saw a host of chances go begging in a nevertheless creditable 72 that kept him at even par alongside Day and Willett.
American amateur champion Bryson DeChambeau, so impressive in the company of Spieth on Friday, slipped back to five over with a 77, while Sergio Garcia (81) and Ian Poulter (82) were among six players who failed to break 80.