Blanchet, whose best finish this season was on another island in the Puerto Rico Open, added six birdies to his round of nine-under par 62.
His only dropped shot came on the par-4 fourth, his 13th hole of the round, when he missed the green well to the left at Port Royal.
He led by one shot over fellow Americans Ben Kohles and Danny Walker and Canada's Corey Conners and Ben Silverman on a day when the wind was all over the place, from gusty to calm with a few passing showers.
Looking to improve their positions in the FedExCup Fall standings, two Australians lined up in the tournament, which was won by Lucas Herbert in 2021.
Veteran Aaron Baddeley shot a two-under par 69 to tie for 60th while Cam Davis was a shot further back.
Blanchet is at No. 114 in the rankings, and points are all that matter this time of the year for so many players. Bermuda is one of five tournaments left in the season, and the top 100 keep full status for 2027.
The 30-year-old is near the end of his first full-time season on the PGA Tour after joining the Korn Ferry Tour in 2020. He's looking for his first PGA win after coming close with a second-place finish in the Puerto Rico Open back in March.
After a five foot eagle on the par-5 seventh hole, his other came on the 17th, the shortest par five but with water lurking to the left.
"Yeah. No. 17, I guess that was my last eagle. I hit a great drive," Blanchet said.
He only had about 180 yards in, but left it out far too the right, only to hole the putt from just outside 50 feet.
"Just dripped in on the last revolution," he said.
