Rory McIlroy saw a four-shot lead wiped out as the World Golf Championships - Cadillac Championship set up for a dramatic conclusion at Trump National Doral.
The Northern Irishman came into the final round with a three-shot lead and extended that in the early stages on Sunday as he looked to be making serene progress in his mission to win a third WGC title.
But while he dropped shots on the seventh and ninth to turn in 38, Danny Willett, Bubba Watson and Phil Mickelson all reached the turn in 33 to join him at the top of the leaderboard on ten under.
Adam Scott and Dustin Johnson were then at eight under, with Paul Casey and Jimmy Walker two shots further back.
A win for McIlroy would make him just the third player after Tiger Woods and Geoff Ogilvy to win three WGC titles, while both he and Willett have the chance to complete a European clean sweep in the four events.
McIlroy already holds the WGC - Cadillac Match Play and another European win would add to Shane Lowry's triumph in the WGC - Bridgestone Invitational and Russell Knox's victory at the WGC - HSBC Champions.
Willett, who finished second to McIlroy in last season's Race to Dubai, already has a win this season at the Omega Dubai Desert Classic, while McIlroy is seeking a first title of 2016.
McIlroy quickly saw his lead cut to two shots by Scott as the Australian birdied the first with Willett, Mickelson and Watson all also taking advantage of the par five.
Scott then found the water with his approach to the third to record a double-bogey, and when Johnson hit the same pond off the tee to also drop two shots, McIlroy's lead was four.
More water trouble for Scott resulted in another double-bogey on the fifth but he picked a shot back up on the next as the leading contenders all made a string of pars.
Willett broke that pattern with an excellent approach for a birdie on the seventh and the lead was cut to two when McIlroy bogeyed the same hole after missing the green with his second - his first bogey in 41 holes.
Watson had made six birdies in a row but he found the green on the par five eighth in two and rolled in a brilliant 60-foot putt to all of a sudden sit just one off the lead.
Playing partner Willett missed a chance to join him from two feet but made amends on the ninth as he put his tee-shot on the par three to 14 feet and rolled in a birdie as both men turned in 33.
McIlroy found the water at the eighth but recovered to save his par while ahead of him Mickelson, who had birdied the same hole, made another gain on the ninth to also get within one.
When McIlroy then found sand off the tee and failed to get up-and-down on the ninth, there was a four-way tie at the top.