Browne, who turned 50 last Friday, is playing in his first Champions Tour event at West Des Moines, Iowa. He had missed five of six cuts on the PGA Tour this season and has been idle since the PGA Transitions Championship in March.
His round Friday included one bogey at the 10th hole, birdies at the third and sixth and back-to-back birdies at the 15th and 16th.
"I'm really happy I got off to a nice start," the three-time winner on the PGA Tour said. "I'm more relaxed out here."
Vaughn was the early leader and overall, 52 players are within five strokes of the co-leaders.
Defending champion Jay Haas shot 1-over 72.
Haas also contended at last weekend's Senior PGA Championship in Beachwood, Ohio.