Gilder closed with a 2-under 69 to end up at 11-under-par 202. Allen Doyle finished two strokes further back at minus-9 thanks to a final round 5-under 66.
Stadler was quoted earlier in the season as saying he wanted to win fast once on the Champions Tour.
'I wouldn't have said a word the first five months this year I was playing so bad,' said Stadler. 'Things have obviously changed and today was a perfect example. I didn't hit the ball that well today, but made a few putts at the right time. I kind of just hung in there. It certainly wasn't pretty.'
Stadler, who matched the course record Saturday with a 7-under 64, put things out of reach quickly on Sunday. Gilder briefly moved within one stroke with a birdie at the second, but Stadler quickly answered.
Stadler birdied the third to regain a two-shot advantage. He stretched it to three shots when he birdied the par-5 fifth and his lead grew to four when Gilder bogeyed the par-4 seventh.
The 50-year-old Stadler saw his lead drop back to three when Gilder birdied the eighth. Stadler extended the margin to five shots with an eagle from 18 feet out at the 10th.
Stadler, who won the Senior Players Championship and the Greater Hickory Classic earlier this year, saw his lead grow to six shots when Gilder bogeyed the 11th.
Gilder tried to make things interesting down the stretch at Oak Hills Country Club. He birdied the par-4 14th to move back within five shots. Stadler birdied the next though to make it a six-shot advantage.
Gilder rolled in a lengthy birdie putt on the 16th before Stadler bogeyed the 17th as they headed to the last hole with Stadler up four strokes. Gilder, however, pulled his tee shot left and was unable to put pressure on Stadler.
Stadler dropped his tee ball on the green and two-putted for the victory.
Stadler said the difference in his season came at the Senior PGA Championship at Aronimink, his first event on the Champions Tour.
'I think Aronimink really helped me,' said Stadler, who picked up $225,00 for the win. 'It was my first week out once I got on the Champions Tour and it was a good, hard, long golf course. I played very well all week in the tough conditions. That was the first time I put more than two decent rounds together since August 2002.'
Gilder mixed two birdies and a bogey over his opening nine, while also doing the same on the back side.
Tom Watson, who nearly aced the par-3 18th, closed with a 2-under 69. He shared fourth place at 8-under-par 205 with Walter Hall (69), Hale Irwin (67), Fuzzy Zoeller (68) and Tom Kite (67).
Dana Quigley, the 2002 champion, closed with a 4-under 67. He shared 22nd place at 3-under-par 210.