Bill Haas of the United States celebrates after winning the Tour Championship and the FedEx Cup in a sudden death playoff with Hunter Mahan at East Lake Country Club, during the final round of the Tour Championship PGA golf tournament in Atlanta, Georgia, Sept 25, 2011. [Photo/Agencies]

ATLANTA - A frenetic, wildly unpredictable final day at the Tour Championship ultimately ended with Bill Haas winning both the tournament and FedExCup honours, though it took a while for his double success to sink in.

The 29-year-old American sealed victory by beating compatriot Hunter Mahan in a sudden-death playoff but he did not realise he had also scooped the season-long playoff jackpot of $10 million until the trophy presentation.

"We did some TV interviews up in the grandstands there on 18 and both trophies were there," Haas told reporters after clinching his third PGA Tour title.

"And there was no other player, so I kind of assumed," he added, sparking widespread laughter in the interview room. "I looked at my wife and she nodded her head, so that was when I realised."

Every player in the elite field of 30 began the week with a mathematical chance of winning the FedExCup and on Sunday points leader Webb Simpson and British world number one Luke Donald were among the likeliest.

However they both fell short, Simpson finishing 22nd when 18th place would have earned him the $10 million bonus while Donald came ever closer, tying for third when outright third would have done the trick.

"I knew $11 million was on the line somehow, whether Luke Donald won it or Webb Simpson won it or I won it, it was there, so that was in my head," said Haas.

"When I was putting for that four-footer to win, it was just to win the Tour Championship, knowing that was all I could do."

Haas played with Donald in Sunday's final round at East Lake Golf Club and he initially thought the Briton had wrapped up playoff honours after finishing with three birdies in the last five holes.

Luke Donald of Britain reacts reacts to his shot off the 17th fairway at East Lake Country Club, during the final round of the Tour Championship PGA golf tournament in Atlanta, Georgia, Sept 25, 2011. [Photo/Agencies]

Donald congratulations

"He birdied the last, and I thought that won the FedExCup for him," Haas explained. "So afterwards I told him, 'Congratulations, I hope that won it for you, I just hope maybe I can win this tournament'.

"I was fortunate to get in a playoff. It was my third one this year and I was 0 for 2 coming into this one. But I told myself it's not over until it's over.

"I could hole this chip, anything can happen. And I did. It was somewhat of a learning experience for me because anything did happen."

Haas was watched on Sunday by his father Jay, a successful Champions Tour player who triumphed nine times on the PGA Tour.

"When my dad watches, I seem to perform maybe a little bit," Haas said with a grin.

Haas comes from a family of accomplished golfers. His great uncle Bob Goalby won the 1968 Masters.

Jay also happens to be an assistant to United States Presidents Cup captain Fred Couples and his son may have done enough at East Lake to earn the final wildcard pick on the 12-man team.

Couples will announce his two picks on Tuesday to complete the 12-man team to take on the Internationals at Royal Melbourne in Australia from Nov. 17-20. He has already promised one of those spots to Tiger Woods.

"I'm not going to say it gets me to Australia," said Haas. "It definitely puts me in the talk up there ... I did what I could do.

"I would love to represent the United States in the Presidents Cup and play for Fred Couples."