Rory McIlroy picked up birdies on the first two holes, but they were not enough to keep him in the lead at the Deutsche Bank Championship as South Africa's Louis Oosthuizen took charge at TPC Boston.
With rounds of 65, 65 and 67 the Holywood man could quite rightly expect to be leading, but he reckoned without the brilliance of the South African.
A sparkling round of 63 saw him leapfrog McIlroy and set up a fascinating final round shoot-out.
Oosthuizen was simply inspired, notching up a a run of seven consecutive birdies to complete the front nine in 29 strokes.
He eventually signed for an eight-under-par 63 to establish a three-stroke lead on 19-under.
Incredibly McIlroy found himself trailing at one stage by seven shots and will have been left scratching his head after having done little wrong. He eventually closed the gap to get up to 16-under, while Tiger Woods remains in contention on 13-under.
It looked like McIlroy was in the mood to create the day's headlines when he fashioned an early eagle chance at the second and when both he and Oosthuizen settled for birdies there was little sign of what the South African was about to produce.
From hole four he embarked on a run of six back-to-back birdies prior to the turn, extending that run to seven at the 10th.
Meanwhile, Richie Ramsay claimed the second European Tour victory of his career after winning the Omega European Masters title by four shots at Crans-sur-Sierre in the Swiss Alps.
The Scot followed up a blemish-free 64 in his third round with a five-under-par 66 to finish 16-under overall yesterday.
Shane Lowry finished best of the Irish in joint-49th on two-under overall, but will be disappointed with his two-over-par final round of 73.
Michael Hoey finished a shot further back in 55th after a 72, with Darren Clarke making up for Saturday's 74 with a one-under-par 71 to go to the clubhouse on four-over and a share of 71st place.