A winner on both the Champions Tour and PGA Tour in consecutive weeks in July, Stadler had eight birdies against just one bogey on the Oak Hills Country Club course. He is at 11-under 131, two strokes better than Bob Gilder.
"I'm glad I have a little cushion heading into tomorrow," Stadler said. "I've found a little comfort zone and learned to score again. It's amazing what a little confidence does."
Stadler has won twice on the elder circuit this season. He claimed the Senior Players Championship in July and the Greater Hickory Classic three weeks ago.