Chad Campbell, Robert Gamez, Jerry Kelly and Jose Coceres shared third place at 3-under-par 68.
Howell, who earned his first career victory on the PGA Tour at last year's Michelob Championship at Kingsmill, played the back nine first at the Copperhead Course at Westin Innisbrook and broke into the red with an eagle at the par-5 14th.
'The golf course was very tough today,' said Howell. 'It will reward a good shot, but it's one of the tougher and one of the better courses that we play.'
The 24-year-old dropped a shot with a bogey at the 16th but managed to respond with a birdie at the 18th.
Howell dropped his third shot from a bunker within six feet for a birdie at the first and hit a brilliant approach inside two feet at the par-4 second. Howell tapped in the birdie putt to make it three in a row.
He stumbled with a bogey at the third but ran home a 30-footer for a birdie at the par-3 fourth.
At the par-4 seventh, Howell hit his second shot to 25 feet and drained the birdie putt to secure the opening-round lead.
Howell, who is currently 27th on the PGA Tour money list, hasn't posted a top-10 finish since The International but the Augusta native is in position to gain a spot in the Tour Championship next week.
'You just go play golf,' said Howell. 'At the end of the day you add them up and you see where you stand. Every time I have ever thought about a position on the money list or any time I ever looked around me and who was around me I have always done worse.'
Forsman did his damage on the inward half with three consecutive birdies starting at the par-3 13th.
At the par-4 18th, Forsman knocked his approach to four feet and converted the birdie putt to finish alone in second.
'I don't think you ever beat this place, it's got enough holes out there,' said Forsman. 'You are always at the edge of your seat if you will. It's going to demand everything you got.'
Gamez tallied six birdies and three bogeys for his share of third.
'I have had some success out here,' said Gamez. 'It's always been one of my favorite golf courses to play.'
Davis Love III, J.J. Henry, Duffy Waldorf, Retief Goosen and Steve Lowery finished in a tie for seventh at 2-under-par 69.
Vijay Singh, who could wrap up the money title with a victory this week, was one shot further back in a group at 1-under-par 70 that features Ernie Els.
Defending champion K.J. Choi was one shot further back in a group at even-par 71.
Phil Mickelson, who needs a strong finish this week to work his way into the Tour Championship, gave those hopes a severe blow on Thursday after he opened with a round of 9-over-par 80.