'When I walked out of my room this morning, I was thinking about withdrawing,' said the 56-year-old Gilder, a nine-time winner on the 50-and-over tour. 'My back went out on me. I was very skeptical about what was going to happen today.'
But a morning visit to a chiropractor at the course fixed him up, and the late surge gave him a two-stroke lead over first-round leader Scott Hoch at 10-under 134.
Steve Ballesteros struggled again in his first Champions Tour start, following his opening 78 with an 81. The five-time major winner was last in the 78-player field at 15 over -- 25 strokes behind Hoch.
Hoch, who held a three-stroke cushion after the first round, lost his lead for the first time with a bogey on the 17th hole at Ross Bridge after Gilder's 8-foot birdie putt. Hoch fell to two strokes back with a 71 thanks to that two-hole, four-shot swing.
Gilder, who doesn't have a top-10 finish this season, made a nearly 19-footer for eagle on No. 16 to move to 9 under, added the birdie on No. 17 and then matched Hoch with a par on the final hole.
'That was definitely a pick-me-up, that eagle,' Gilder said. 'That was the first really good putt I've made in a while. I missed a few birdie putts before that.'
Gilder hasn't led after two rounds since winning the Constellation Energy Classic in August 2005.
Hale Irwin (68) was three strokes back, and Denis Watson (66) and Fuzzy Zoeller (70) followed at 65 under. Defending champion Brad Bryant (69) topped a large group at 5 under that included former Alabama star Jerry Pate (69).
Still nursing a three-stroke lead, Hoch missed a tap-in putt on the ninth hole and another short one on the 10th for a pair of bogeys. His opening 65 had given him the tour's largest first-round lead of the year, but putting problems cost him.
'Nothing went in, and I missed a bunch of easy ones,' Hoch said. 'The only bogeys I had were little putts I missed.
'Bob played a really good round of golf. He was hitting it close all day.'
Hoch is seeking his second Champions Tour victory two weeks after winning the FedEx Kinko's Classic in Texas.
Gilder, meanwhile, got off to a rocky start with a bogey on the first hole but it was just about the only trouble spot in his round.