The 57-year-old Couples shot a 7-under 65 to reach 11-under 133 on The Old Course at Broken Sound.
Doug Garwood, Joe Durant, Scott McCarron and first-round leader Olin Browne shared the top spot, all birdieing the par-5 18th. Garwood shot 64, Durant 65, McCarron 66, and Browne 69. Tom Pernice Jr. had a 64 to match Couples at 11 under.
Couples birdied the first three holes, dropped a stroke on the par-4 fourth, birdied the par-5 sixth and eagled the par-4 10th. He two-putted from about 100 feet for birdie on 18.
''It was a good round overall,'' Couples said. ''I made some putts, obviously. That's really about it. I didn't do anything overwhelming, but I didn't do much poor. A couple times I got it up-and-down to keep going. I birdied the first three holes and I absolutely butchered the fourth hole from about 80 yards. I came up way short and three-putted.''
He holed out with a wedge on the 10th.
''I forgot about that,'' Couples said. ''I hit a 3-wood and got it way down there and I was surprised, 90 yards, which is a perfect sand wedge. I hit it right by the hole, took a bounce and spun back in. I totally forgot about those fun things. But that was a surprise. Picked up two quick ones there. It kind of pushed me, obviously, close to everybody.''
Couples is playing in Florida for the first time since the 2006 Honda Classic.
''Glad I came,'' said Couples, the Hall of Famer who won the last of his 11 senior titles in 2014. ''The course is beautiful. I've never played here, so yesterday was a little bit of a guessing game because I had never played the course and we got rained out in the pro-am after eight holes. But I got it around and today was much better. I love the course and plan on coming back.''
McCarron won twice last year on the 50-and-over tour.
''A lot less wind today, but some tough hole locations, so it made it play tough,'' McCarron said. ''Yesterday was a lot tougher with the wind, but today was nice. It was windy when we started and then just kind of laid down toward the afternoon. This is such a great golf course and it's in phenomenal shape, so it's going to be a shootout tomorrow.''
Bernhard Langer was tied for 54th after his second straight 71. The 59-year-old German star is coming off a victory in the season opener in Hawaii, his 30th career victory on the PGA Tour Champions. He won the Allianz Championship in 2010.
Defending champion Esteban Toledo was 8 under after a 67.
Winning Ryder Cup captains Jose Maria Olazabal and Paul McGinley are making their senior debuts. Olazabal was tied for 23rd at 6 under after a 67, and McGinley was tied for 44th at 3 under after a 73.
John Daly eagled the 18th in a 75 that left him tied for 69th at 2 over.