"There just aren't words to explain how I feel," said Ahern, who birdied the final two holes of regulation to force the playoff with the senior tour's career money leader.
"I'm sure this is old hat for Hale but this is new hat for me, believe me. When I played on the PGA Tour years ago, I wasn't very good. Now to beat Hale Irwin to beat the best is pretty special."
It was the second week in a row, Irwin, a five-time champion this year, lost in a playoff to a first-time senior winner. Tom McGinnis beat Irwin last week at the BankBoston Classic.
"The last two weeks, guys have made putts on the last hole to force playoffs that's tough to take," Irwin said. "But that's the senior tour dreams can come true. I thought I'd win if I didn't do anything silly and I didn't do anything silly. But then he made that putt on 18."
The 50-year-old Ahern, a qualifier whose previous best finish was an 18th, won the $202,500 top prize as well as a one-year exemption from qualifying on the senior tour.
"I'm not going to miss going out there on Monday," said Ahern, who has earned $268,050 50th on the money list in his first senior season.
"You don't know how you're going to do when you're under the gun. When you look at my past in pro golf, there's not much to draw on. I just tried to stay focused and play one shot at a time. I'm really proud of myself for doing that."
Ahern, who played on the PGA Tour from 1972-75 and now runs a company that organizes executive golf events, became the seventh qualifier to win on the senior tour.
He birdied the last two holes in regulation, including a 15-footer from the fringe on the 72nd hole to force the playoff as he and Irwin finished at 16-under 272 at Richelieu Valley Golf Club.
Ahern had a final-round 68 Sunday, while Irwin, the third-round leader, had a 69.
Irwin saved par after driving into the trees on the left on the first playoff hole. He was in the trees on the right on the second and then hit into a bunker.
Ahern missed a 15-foot birdie putt on the second hole, but Irwin missed a 6-footer for par. Ahern broke into tears after making his 5-foot par putt for the victory.
"I didn't have many good tournaments on the PGA Tour," Ahern said. "I didn't know where the ball was going. The best place for me was off the tour. I didn't belong there. But I belong here. I'm so much of a better player now."
Irwin, 54, the senior tour's player of the year the last two seasons, has 26 wins in five years on the over-50 circuit after wining 20 times, including three U.S. Opens, in his days on the PGA Tour.
"I'm just not playing well," said Irwin, who said he will take two days off to combat fatigue before next week's event at Kansas City. "Five birdies in the last two rounds is not enough."
"I didn't deserve to win. It seems that if you want to enhance your career, play me in a playoff. It works. That's two weeks in a row."
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