Dunlap closed his bogey-free round on Omni Tucson National's Catalina Course with birdies on the par-5 eighth and par-4 ninth.
"I was thinking going into this week, I haven't used up much of my good golfing quota at Tucson National over the years," Dunlap said. "We played here in college, I played mini-tour events here, I played regular tour events here, and now I'm playing the PGA Tour Champions here. I've always liked the golf course. I've done OK, but nothing great. So, today was kind of special to hit it good and make some putts, too."
Tolles, playing in the last group off the first tee, birdied the par-4 18th for a share of the lead. He also had a bogey-free day.
"All in all, very happy with 8 under," Tolles said. "I haven't played a lot of competitive golf the last 10 years, so it was kind of a learning experience."
Stricker played the four par 5s in 5 under, with an eagle on the second and three birdies.
"We're only a third of the way done," Stricker said. "It's a long ways to go yet, but a good start, which I'm happy about. Hopefully, put two more up just like that."
Stricker finished second last year in his senior debut. The 12-time PGA Tour winner tied for second two weeks ago in Florida in the Chubb Classic, his fifth top-three finish in seven career senior starts.
University of Illinois coach Mike Small matched Stricker at 66.
"I made some putts today," Small said. "I've got to be a little stronger tomorrow with some of my around-the-green shots."
Stricker played at Illinois and has known Small for more than 30 years.
"He's doing a bang-up job at Illinois in the golf program, and he plays well," Stricker said. "We're giving him a spot again at our tournament in Madison to come up and play. He's a good guy. He still plays great golf and he embodies everything a professional golfer and a good person should be, so it's cool to see him playing well."
Langer birdied three of the last four holes, holing a 60-footer on 18. The 60-year-old German star won seven times last season, three of the victories in majors.
"Just trying to get my game in shape where I have a lot of confidence in everything, the long game, the short game, and then hopefully take that into the Masters," Langer said.
Defending champion Tom Lehman, playing alongside Stricker, had a 71.
Len Mattiace also shot 71 in his senior debut. The two-time PGA Tour winner turned 50 in October.
Vijay Singh opened with a 72.
John Daly was last in the 78-player field with an 80. He had one birdie, six bogeys and a double bogey on the par-5 15th.