Nelson, who has 16 wins on the Senior Tour, shared second place with Jack Spradlin, Wayne Levi, Dave Eichelberger and Tom Jenkins.
Fresh off his third victory on the elder circuit, a playoff win over Hale Irwin at the SBC Senior Open, Gilder took to Nashawtuc Country Club with momentum on his side, and it showed on the back nine.
After he picked up only one birdie over the first nine holes, Gilder torched the inward half to take the outright lead.
'I went out a little cautious,' said Gilder. 'I gained some momentum as the round went along.'
Gilder chipped his third shot inside 12 feet for a birdie at the par-5 10th. He made it two in a row with a birdie at the 11th and drained a 30-footer for birdie at the 14th to reach 4-under.
At the par-4 16th, Gilder landed his approach within 14 feet of the hole for his fifth birdie of the day to join a logjam at 5-under.
Gilder took sole possession of first at the par-5 last. The 51-year-old played it safe and after a lay up, he dropped his third inside four feet to complete a bogey-free round.
'I'm not doing anything really bad right now,' said Gilder. 'I'm keeping myself in play and out of trouble. I have good vibes here. Nashawtuc gives you several options. You can cut some of the doglegs or lay back and have some longer shots onto the greens.'
Nelson has enjoyed tremendous success at Nashawtuc. His 67 Friday was his fifth straight round in the 60s. He got off to a fast start with a stretch of four consecutive birdies starting at the third.
Nelson reached 5-under with a birdie at the 10th but ran into trouble with a bogey at the par-3 13th. He responded at the following hole where he hit a wedge to eight feet and converted the putt for his sixth birdie of the day.
'I didn't know what to expect coming in this week,' said Nelson, who is seeking his first win of 2002. 'I've played decent, but not good enough. That's the way today went.'
Allen Doyle, winner of the 2001 Charles Schwab Cup, collected six birdies and two bogeys for a round of 68. He finished alongside Australia's Rodger Davis in a tie for seventh.
Jim Thorpe, Jay Sigel, George Archer, Walter Hall, U.S. Senior Open champion Don Pooley, Hubert Green, Jim Colbert and Ted Goin are knotted at 3-under-par 69.
Irwin, a two-time winner of this event, finished fives shots off the lead in a tie for 21st at 1-under-par 71.
Arnold Palmer, who won this event in 1982, posted a 3-over-par 75 that included an eagle at the par-5 10th.
Full-field scores from the FleetBoston Classic