The 51-year-old Oregon native, who was named the Senior Tour's 2001 Rookie of the Year after winning twice and posting 11 other top-10s last season, set a new course record with a nine-under-par 63 at the Port Course at Harborside International, which is hosting this event for the first time.
Gilder closed with seven straight threes -- two pars, four birdies and an eagle at the par-five 18th -- to claim the top spot at 11-under-par 133.
'Things were working today,' said Gilder. 'I figured something out at the practice tee and the momentum just built as the round went along. Everything fell into place.'
Bobby Wadkins spread seven birdies around a bogey-free 65 and took over second place at 10-under.
Dick Mast, who shot 64 seven times while on the PGA Tour, carded that number Saturday thanks in big part to a run of six birdies in a row. He moved into a tie for third at eight-under 136 with John Mahaffey (65) and Tom Wargo (69).
Gilder began the second round four shots out of the lead but made his presence felt with three birdies in the front nine. He made the turn at five-under and, after parring the first two holes on the back, knocked a nine-iron to three feet for a birdie at the 12th. Two holes later Gilder rolled in a 10-foot putt for birdie to get to seven-under par.
Gilder parred the 195-yard 15th but stuffed his approaches in tight for back- to-back birdies at 16 and 17.
'I nearly knocked the flag down on two of the last three holes,' he said.
After knocking his second shot with a three-wood to the fringe at the 522-yard finishing hole, Gilder sank a 20-foot eagle putt to match his low round on the 50-and-over circuit.
Two weeks ago at the Canada Senior Open, Gilder established his senior best with an eight-under 63 in the second round en route to a fifth-place finish. It marked his eighth top-10 showing of the season, with his best result a tie for second at the Siebel Classic in March.
Wadkins, who became the youngest winner in Senior Tour history (50 years, 10 days) at last year's Long Island Classic, has three runner-up finishes already this season, including a share of second at the Senior PGA Championship.
Mast has struggled in 2002 with just two top-10s in 18 starts, but racked up a total of 10 birdies Saturday. His six-birdie streak -- the second-longest on tour in this year -- stretched from the eighth to the 13th, and featured four putts from inside five feet and a 35-footer at the par-four 10th.
'I switched putters yesterday and I seemed to roll the ball better today,' said Mast, who took 25 putts Saturday as compared to 33 in round one.
Although Mast has never won on the PGA or Senior Tours, he did record four victories on the Buy.com Tour.
Rodger Davis (69), Terry Mauney (69) and Roy Vucinich (70) were in sixth place at seven-under-par 137.
Hale Irwin, a three-time winner of this event, finished five strokes off the pace after a one-under 71. Just one shot back after opening with a five-under 67, Irwin actually slipped to two-under through 12 holes Saturday but produced four birdies over the final six holes.
First-round leader Ted Goin bogeyed two of his first three holes and dropped into a tie for 14th place at minus-five. He posted a second-round 73.
Defending champion Dana Quigley, who shot himself out of the tournament Friday with a six-over 78, notched his second hole-in-one on the Senior Tour on his way to a 69 on Saturday. He used a seven-iron from 163 yards to ace the par- three 13th. Quigley will begin the final round 14 shots back at three-over.
Full field scores from the SBC Senior Open