At the SBC Senior Open last week, Gilder out-dueled Hale Irwin to win the title on the first extra hole.
Gilder and Mahaffey returned to play the 18th for a third time. Mahaffey hit his third shot to the green but the ball rolled back to the front of the putting surface and stopped 35 feet from the hole.
Gilder played his second shot just short of the green and hit his third inside three feet. He drained the short birdie putt for his second straight win and his fourth on the Senior Tour.
'This win is overwhelming,' said Gilder, who became the first wire-to-wire winner in the history of this event. 'I didn't expect this one. I really enjoy this golf course. I can't quite comprehend winning two in a row yet.'
Gilder moved to 3-0 in career playoffs. The last of his six PGA Tour victories came at the 1983 Phoenix Open after an eight-hole playoff with Johnny Miller, Mark O'Meara and Rex Caldwell.
'I was very lucky to play today,' said Mahaffey, who battled back spasms in Sunday's final round. 'I didn't think I was going to be in a playoff. Bob played well and deserved to win.'
On Sunday, Gilder finished regulation tied with Mahaffey at 13-under-par 203 after a bizarre turn of events at the 72nd hole.
Mahaffey, playing three groups ahead of Gilder, landed a brilliant third shot onto the par-5 closing hole inside two feet. He made the birdie putt to complete a round of 65 and enter the clubhouse at 13-under with Gilder and Jim Thorpe still battling it out on the Nashawtuc Country Club layout.
Gilder reached 14-under with a birdie at the 17th and stepped onto the tee at the 18th with a one-shot lead over Thorpe and Mahaffey. Gilder, who had not made bogey all week, found trouble when his second shot traveled over the green and into heavy rough. He failed to get up and down and fell back to 13-under, opening the door for Thorpe.
'I thought my shot at 17 was going to do it, but the gods had something different in mind,' said Gilder.
Thorpe, who won the first major of the season at The Tradition in April, played his second shot short of the putting surface and chipped onto the green to set up a four-foot birdie putt for the win. He lined up the putt but ran the ball past the hole. Thorpe now needed to convert just to make the playoff but his par attempt skimmed the edge.
'I had a four-footer downhill and the putter exploded,' said Thorpe. 'First time I've really choked. The second putt was longer than the first. I just missed it.'
Gilder and Mahaffey returned to the 18th tee to begin the playoff and both made par in different fashion. Mahaffey had no choice but to lay up and he nearly holed out with his third shot as the ball spun back to stop 15 feet from the hole where he two-putted for par. Gilder went for the green in two but found a greenside bunker from which he saved par.
The duo moved onto the par-3 17th and Mahaffey knocked his ball pin high. Gilder was not as fortunate as he barely reached the front edge of the green. However, both players again could do no better than par.
Thorpe carded a final-round 70 to finish at 12-under-par 204 alongside Dave Eichelberger. Larry Nelson, who won this event in 2000 and 2001, was one shot further back at 11-under-par 205 along with Wayne Levi.
Final results from the FleetBoston Classic