'I played well today, but who knows what the next couple of days will hold for me,' said Fleisher. 'This is a good course for me because you don't have to overpower it here. It's a very playable course for my type of game and I felt comfortable out there.'
Jay Sigel, James Mason, David Eger, John Harris and Dick Mast finished three shots off the lead in a tie for third at 4-under-par 67.
Play was delayed for almost an hour early on but the wet conditions didn't matter to Fleisher, who parred his first three holes at Nashawtuc Country Club before running off three consecutive birdies starting at the par-4 fourth.
He drained a 15-foot putt for birdie at the par-4 ninth to make the turn at 4-under and continued his fine play on the inward half with a birdie at the par-4 11th after his approach landed within five feet of the cup.
Fleisher hit a wedge to 15 feet for a birdie at the par-4 14th and secured sole possession of the opening-round lead at the par-5 last after he dropped an 8-iron within three feet of the cup for a closing birdie.
'This was very, very unexpected,' said Fleisher, who won this year's Verizon Classic. 'I haven't done much in the last couple of weeks. I'm not sure what it is here in Massachusetts.'
In 1991, Fleisher picked up his lone PGA Tour victory at Pleasant Valley Country Club in Sutton, Massachusetts.
'If I didn't win at Pleasant Valley who knows where I'd be now,' said Fleisher, who also won the U.S. Senior Open when it was staged in Massachusetts in 2001. 'It was a life turnaround for me.'
Purtzer picked up three birdies over his first 10 holes and came on strong down the stretch.
He tallied back-to-back birdies starting at the par-4 15th and hit out of a bunker to eight feet for a birdie at the 18th to finish one shot off the lead.
'The rain really softened up the course,' said Purtzer. 'The fairways got a lot bigger and the greens accepted the shots a lot better. I'm a real fan of the course. It's a neat course.'
Defending champion Bob Gilder finish four shots off the lead after a round of 68. Gilder, who has one victory to his name this year at the Emerald Coast Classic, was joined by D.A. Weibring, Ed Fiori, Dave Barr, Dana Quigley, Ted Goin, Allen Doyle, Bobby Wadkins and Dave Stockton in a tie for eighth.
Craig Stadler and Doug Tewell were one shot further back in a group at 2-under-par 69.
John Mahaffey, who lost this event in a playoff to Gilder last year, collected two birdies and two bogeys to finish in a tie for 37th at even-par 71.