Two-time U.S. Open champion Retief Goosen, American Ryder Cup captain Tom Lehman, Charles Howell III, Dean Wilson and Ben Crane are knotted in second place at 4-under-par 67.
Brehaut began the opening round on the back nine at the Copperhead Course and broke into red figures at the par-5 11th. His 3-wood second sailed over the green, but he chipped inches from the hole and tapped in for birdie.
The 42-year-old dropped a shot at the 13th, but made up for the mistake with a birdie at the very next hole. Brehaut parred his final four holes on his opening nine to make the turn in 34.
Brehaut started his second nine in style at the par-5 first. He drained a 30-foot, hard-breaking eagle putt at the 560-yard opening hole to reach 3 under par for the championship.
He collected back-to-back birdies from the third, then broke out of the pack at the seventh, his 16th hole of the first round. Brehaut rolled in a 45- footer for birdie to claim the opening-round lead.
'Today I drove it in the fairway, which you've really got to do out here,' said Brehaut. 'I made a bunch of putts today. It was the best putting day I've had in a couple of months.'
Brehaut has some great history at this golf course. Last year, Brehaut ran home a curling putt on the 72nd hole to move into the top 150 on the tour's money list. That allowed him to skip the second round of the Qualifying School, where he ultimately retained his card.
'It all came down to the last putt,' said Brehaut. 'It was probably the fastest putt on the course, downhill, left-to-right. That was a big round for me.'
Brehaut does not have concerns like that this year at Innisbrook. He finished third at The International and tied for fourth at the Deutsche Bank Championship.
He is 61st on the money list and instead of worrying about his card, he's hoping for bigger things. The top 40 at the end of the year receive an invitation to the Masters and Brehaut is also trying to get into the top 30 for a spot in next week's Tour Championship.
'For whatever reason, my swing got a little out of sync (after the Deutsche Bank Championship),' acknowledged Brehaut. 'I missed a couple of cuts and didn't make much money. But this is an important week to move back up.'
Last week's Funai Classic at Disney World winner, Lucas Glover, Davis Love III, Bernhard Langer, Jesper Parnevik, Steve Allan, Peter Lonard, Billy Mayfair and Rocco Mediate are knotted in seventh place at 3-under-par 68.
This is an extremely important week for some players, Mediate included. There is only one full-field event left on the schedule, next week's Southern Farm Bureau Classic, so only two chances remain to get into the top 125 on the money list and secure cards for next year. Mediate sits at No. 125.
Defending champion Vijay Singh struggled on Thursday. He was 1 under par when he reached the par-4 16th tee. Singh pushed his tee shot into the water and made a double bogey. The No. 2 player in the world bogeyed his final two holes and shot a 3-over 74, which is good for a share of 104th place.