Trying to win for the third time in four career starts on the 50-and-over tour, Mickelson had seven birdies and a bogey at the Donald Ross-designed Timuquana Country Club course in the round interrupted by a rain delay.
"Because of the rain, a little bit of some balls that would plug or maybe get a little mud, but it was really in great shape," Mickelson said. "They did a great job of getting the course ready, and draining it so quickly for us to go back out and play, that was really nice."
Mickelson played the front nine in 5-under 31 and added birdies on the two back-nine par 5s before dropping a shot on the par-4 18th.
"I wasn't quite on when we got back out there, I just was a little bit off," Mickelson said. "I hit a few wayward shots. I just didn't feel great, but fought to finish the round off and try to regroup for tomorrow. It's a good start, though. I didn't do any damage and made some good birdies on that front nine and I'll try to get that level of play back for tomorrow."
The 51-year-old Mickelson won the PGA Championship in May at Kiawah Island for his 45th PGA Tour title and sixth major championship. Last year, he opened his senior career with consecutive victories in Missouri and Virginia. Lefty tied for 20th in Tucson, Arizona, in February in his lone Champions event this year.
"I like the fact that it's 54 holes," Mickelson said. "It's not anywhere near as mentally and physically draining as the regular tour and you don't have to be as perfect as on the PGA Tour because the penalty for miss is so much greater there."
Gogel birdied the last two holes. Playing his first Champions season, the 50-year-old Gogel won at Pebble Beach in 2002 for his lone PGA Tour title.
Frank Lickliter II and Cameron Beckman were tied for third at 67. Charles Schwab Cup leader Bernhard Langer was at 68 with Darren Clarke, David Toms, Tim Herron, Kevin Sutherland, Rod Pampling, Robert Karlsson and Steven Alker.