Thatcher was joined atop the leaderboard by James Driscoll and Richard Swift at StoneWater Golf Club.
Kyle Thompson, who won The Rex Hospital Open earlier this year, posted a 5- under 66. He shares third place with Scott Gardiner, Willie Wood, David McKenzie, Matt Hansen and Kenneth Staton.
Thatcher, who claimed his second tour win last week at the Peek'n Peak Classic, tripped to a bogey on the second. He came right back with a 30-foot birdie putt on the third.
The 30-year-old made it two straight with a two-putt birdie on four before getting to minus-2 with a 10-foot birdie effort at the fifth.
Thatcher, who has three straight top-10 finishes and top-25s in nine of his last 10 starts, kept rolling with 8-foot birdie putts on the seventh, ninth and 12th.
At the long par-5 13th, he knocked a wedge to 12 feet to set up birdie. Thatcher sank another 8-footer for birdie at 14 to get to 7-under. He slipped back into a share of the lead with a bogey on the 17th.
'I played a really good round of golf today,' Thatcher stated. 'The wind came up and scores were going to be tough to come by, so to finish up with 6-under is a good start to the week.'
Driscoll, who collected his lone tour win in 2004, started on the back nine. He birdied four of five holes from the 14th, but dropped a shot at the first. Driscoll came back with birdies on three and four. He grabbed a share of the lead thanks to a birdie at the par-4 eighth.
'My iron play was really solid, but I drove it all over the place,' admitted Driscoll. 'Obviously, I putted well, but I've got some work to do off the tee. I'm finally making some putts and playing some clean rounds.'
Swift also started on the back nine. He flew up the leaderboard with three straight birdies from the 10th. Swift stumbled to a bogey at the 17th, but rebounded with a birdie on No. 1. He birdied three of four holes from the fifth to grab a piece of the first-round lead.
'I said to myself at the beginning of the week that I was going to make it two seasons,' said Swift, who missed has nine of 10 cuts and withdrew from another event so far this season. 'The first one is over, thankfully, and the new season starts in July. I typically play better towards the end of the year anyway.'
Nicholas Thompson, who won earlier this year in New Zealand, opened with a 4-under-par 67. He is tied for 10th with Joe Daley, Jimmy Walker, Erik Compton, Curtis Malm, Tee McCabe, D.A. Points, Hunter Haas, Dave Rummells and Martin Laird.