Rafael Gomez and Robert Garrigus share second place at 6-under-par 66, followed by former PGA Tour member Carl Paulson and Kevin Muncrief, who opened with rounds of 67.
Boros opened on the back nine Thursday and broke into red figures in an unconventional manner. He holed out a 7-iron from 164 yards at the 13th for an eagle.
'It looked good all the way,' said Boros, who plays on the PGA Tour but was not qualified to tee it up at the Players Championship. 'That eagle kickstarted my round.'
Boros, a two-time winner on the Nationwide Tour last year, traded a birdie for a bogey through the rest of his first nine. On the back side, Boros birdied three of his first four holes, then eagled the par-5 seventh to take the first-round lead.
'I'm excited about playing golf again,' said Boros, who nearly withdrew before the tournament to be home with his sick children. 'I hit it real well and had a lot of good birdie chances today. I'm glad I came. But it was tough leaving my kids.'
Gomez recorded seven birdies and one bogey in his opening round, which was impressive considering how tough the Argentinean found Le Triomphe to be on Thursday.
'The course is not playing easy,' said Gomez. 'Hitting the driver well was very important today. I also made a lot of putts and hit my irons well.'
Garrigus was only 1 under through his opening nine, the back nine at Le Triomphe. He collected five birdies on his second nine to get within one of the lead.
'I sprayed it on the front but ended up getting in at 1 under,' said Garrigus. 'Then on the back side I really got the juices flowing which was nice.'
Jeff Gove, Ryan Hietala and Charley Hoffman are tied for sixth place at minus-4.
Defending champion Brett Wetterich struggled on Thursday with a 3-over 75.