'This golf course is so much fun to play,' said Overton, winless on the PGA Tour. 'It's really challenging. If you're hitting it great, you can have scoring opportunities. I'm just having a blast.'
Bo Van Pelt was a stroke back after a 64, and Mark Wilson (66), Stewart Cink (66), Jimmy Walker (67) and Jhonattan Vegas (69) followed at 9 under. First-round leader Robert Allenby followed his opening 63 with a 72 to drop into a tie for ninth at 7 under.
The jet-lagged Overton, a last-minute replacement for David Duval, had a chance to take the outright lead on the final hole, but missed a 7-foot birdie putt.
'I changed golf clubs a couple of weeks ago and my ball-striking has improved so much. Today everything clicked,' said Overton, the 28-year-old Indiana player who had a scare before the tournament when his clubs didn't arrive until late Wednesday.
Overton eagled the par-4 15th, hitting a driver to 6 feet.
'I watched Mark Wilson hit it right at the stick, and I'm like, wow, this is a great little hole. Maybe I can hit my driver, too,' Overton said. 'I just hit it right at the pin. It came off just perfect, laying there on the front of the green and it rolled up there to 6 feet for eagle.'
Jacobson won the Travelers Championship this summer for his first PGA Tour title.
'The driving has been setting up a lot of opportunities,' Jacobson said. 'I've been driving it well and on this course, if you drive it on the fairways, it's not overly long and it gives you opportunities.'
He saved par on 18 after hitting to a foot from a greenside bunker.
'Growing up, I spent a lot of time in the rough, in the bunker, in different lies. Like in the backyard, I would try to chip over a stone wall,' Jacobson said. 'I played a lot of weird shots through my youth and I think that by challenging myself that way, I have learnt a lot of different shots, which come in useful.'
Three-time major winner Vijay Singh followed his opening 72 with a 64 to reach 6 under.
Defending champion Ben Crane was 5 under after a 68.
The winner will receive $1.3 million from the $6.1 million purse.