Rory McIlroy and Tiger Woods both suffered defeat on day one of the Turkish Airlines World Golf Final.
McIlroy, who had not touched a club since the Ryder Cup came to such a thrilling climax nine days ago, unravelled spectaculary over the closing holes to lose to Matt Kuchar while Tiger Woods lost by a shot to 2011 Masters champion Charl Schwartzel.
McIlroy made two eagles in an up and down outward half of 34 and, although Kuchar pulled three shots clear with a birdie at 10, the match was in the balance with four to play.
However, world number one McIlroy fell apart in dramatic fashion, going triple bogey, double bogey, double bogey from 15-17 to slump from two-under to five-over in the medal match play format where the lowest strokeplay score over 18 holes wins one point.
Kuchar dropped shots too but was able to coast home in one-under 70 to win by six strokes.
Woods fought back valiantly to pull level with Schwartzel after birdies at 16 and 17 but a loose approach into a bunker at 18 led to a bogey five, allowing the South African to win by a shot, 69 to 70.
In the third match, Justin Rose (71) never needed his best to beat American Hunter Mahan (75) who didn't manage a single birdie while a par at 18 saw Lee Westwood (72) edge out American Ryder Cup foe Webb Simpson (73).
Each of the eight players play three matches in the group stages, the remaining two head-to-heads both taking place on Wednesday.
The winner of Group One (Woods, McIlroy, Kuchar, Schwartzel) will then face the runner-up of Group Two (Rose, Mahan, Westwood, Simpson), and vice versa, in Thursday's semi-finals, with the final to be staged on Friday.
McIlroy closed within one shot when Kuchar bogeyed the 13th, but Woods was now four adrift of Schwartzel after also dropping a shot on the same hole.
Mahan and Rose were level on two over after 11 holes, while Westwood had birdied the 10th to improve to two over, two behind US Open champion Simpson.
McIlroy drew level when Kuchar bogeyed the 14th, but the world number one then amazingly played the next three holes in seven over par.
Poor drives, one right and one left, led to a triple-bogey seven on the 15th and a double-bogey seven on the 16th, while a duffed chip on the par-three 17th led to another double bogey.
From two under par McIlroy was now five over and six behind Kuchar with one to play.