cool Bill Haas held his nerve to beat fellow American Hunter Mahan in a thrilling playoff for the season-ending Tour Championship Sunday and also claim FedExCup honors with its $10 million bonus. Haas knocked in a four-foot par putt at the third extra hole, the par-three last, to seal victory with Mahan having bogeyed after hitting his tee shot into a greenside bunker and splashing out 15 feet beyond the cup. The putt earned Haas his third PGA Tour title and a combined total of $11.44 million for winning the richest playoff of all time in golf. “This just worked out for me,” a smiling Haas said greenside at East Lake Golf Club after pumping his right fist in celebration, removing his cap and embracing Mahan. “I'm very fortunate. It is very unexpected.” The pair had finished the 72 regulation holes on eight-under-par 272, Haas squandering a three-shot lead with three holes remaining to close with a two-under 68 and joint overnight leader Mahan carding a 71. British world No. 1 Luke Donald birdied three of the last five holes for a 69 to finish in a tie for third with South Korean K.J. Choi (70) and Australian Aaron Baddeley (72). Several players had a chance of landing the lucrative jackpot going into the final round, with FedExCup points leader Webb Simpson and Donald looking the likeliest. However American Simpson, who would have prevailed over Haas had he finished no worse than 18th on Sunday, ended up 22nd after battling to a 73. Donald, fourth in the standings at the start of this week, would have claimed the $10 million bonus had he finished alone in third. Joint third was not quite good enough. Haas, who came into the Tour Championship ranked a lowly 25th in the elite field of 30, ended up sweeping the honors against the odds. “I don't know how many times I can say the word fortunate, but if Webb plays a little bit better ... all these things had to happen for me to win, and they did,” he said.