The 57-year-old Calcavecchia birdied seven of his first 10 holes and added another on the par-4 seventh at The Old Course at Broken Sound.
"It was, for 10 holes, a spectacular putting exhibition," Calcavecchia said. "I didn't miss, literally, which was nice. And then I lipped one out on 2, which was my 11th hole, and then really never made another one. Kind of lipped one out on 8 about 6 feet. Hit a beautiful shot in there."
Calcavecchia won the last of his three senior titles in 2015. He won the 1989 British Open for one of his 13 PGA Tour titles.
"I could have hit a few more fairways, but some of these fairways aren't that easy to hit, so really good day," Calcavecchia said. "I knew I was playing pretty good coming in. Been feeling pretty good, playing a lot of golf. Great start, obviously."
Rocco Mediate and Jeff Maggert were a stroke back. Mediate eagled the seventh, hitting a 3-wood to 30 feet, but closed with a bogey on the par-4 ninth.
"You've got to get yourself sort in position on this tour on the first day or else you're toast because the scores, as you see, go low," said Mediate, the 2013 winner. "If you're not good the first day, you have no chance."
Bernhard Langer, the 2010 winner in his home event, was at 66 with Fred Funk and Jesper Parnevik. The 60-year-old Langer won seven times, three of them majors, last season.
"I played solid," Langer said. "Made my first bogey when I might have hit my best shot, a 4-iron off the tee that just went further than I thought. Just got to work on my putting a little bit and I should be right there on Sunday."
John Daly, playing alongside Langer, was another stroke back with 2014 champion Michael Allen, 2015 winner Paul Goydos, Steve Flesch, Duffy Waldorf, Kirk Triplett, Jerry Smith and Kent Jones.
"Bernhard always plays good," Daly said. "So when he's playing good, making birdies, you kind of feed off of him. ... When you play with Bernhard, you've got to play good. Somehow or another you've got to find a way because he's always going to shoot under par."
Colin Montgomerie had a 70, and defending champion Scott McCarron shot 73. Charlie Rymer birdied the first two holes in his Champions debut, but had a double bogey and two bogeys on the last six in a 75.
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