They matched the tournament scoring record for lowest first-round score held by six other players.
Dustin Bray, David Hearn, D.A. Points, Ryan Hietala and Garth Mulroy were a stroke behind at 7-under 64.
There were 10 players tied at 65, and 54 overall who were within five shots of the lead on a low-scoring first day at Hillcrest Country Club.
Tadd Fujikawa, the Hawaiian teenager who became the second-youngest player to make a PGA TOUR cut at the Sony Open in January, added another distinction to his fledgling career.
Fujikawa was one of three players to ace the 133-yard 17th hole on Thursday -- the first time in Nationwide Tour history that three players had a hole-in-one on the same hole in the same round.
Making his first Nationwide Tour start -- and third start as a professional -- Fujikawa opened with a respectable 1-under 70 and was tied for 78th place. At 16 years, eight months and 11 days, he was the youngest player in tour history to record an ace.
On the other end of the experience spectrum is co-leader McGovern, a 42-year- old grinder who recalled playing in the first Boise Open in 1990, when it was the Ben Hogan Tour.
He tied for 26th place.
'I still remember making the drive back then from Reno up here to Boise,' said McGovern, who won three times in 1990 and once on the PGA Tour in 1993. 'I'm happy to be back. Sure the circumstances could be different, but I love to compete and I enjoy this event.'
McGovern and Klauk were the only co-leader to post a bogey-free round Thursday, with each player collecting eight birdies. Thompson and Pappas both had an eagle, seven birdies and a bogey.
'Today the golf course played beautifully,' said McGovern. 'The greens played perfect. They were fast. There might be a lot of red numbers, but this course can bite you too.'