Howell, winless since 2002, managed a 4-under 68, highlighted by a strong run on his back nine. Curtis posted a 3-under 69 to join Howell in first at 12-under-par 204.
Hunter Mahan (67), Robert Garrigus (68) and Greg Owen (68) are tied for third place at minus-11. Greg Kraft (66), Bo Van Pelt (67) and overnight co-leader Ryan Moore (71) share sixth at 10-under-par 206 at the Mystic Rock Course at Nemacolin Woodlands Resort & Spa.
Play was delayed almost three hours at the start due to dense fog. Officials shifted things around and sent the players out in threesomes off both the first and 10th tees.
Howell took advantage of damp conditions with birdies at the first and fourth holes. He parred his remaining five holes and added another at the 10th before trouble loomed.
He committed 'unforced errors' with a pair of bogeys at 11 and 12, but reclaimed the lost strokes with back-to-back birdies at the par-4 14th and 15th holes.
At the par-5 16th, Howell knocked his second 20 feet right of the flagstick. He ran home the eagle putt to momentarily take the outright lead at minus-12.
Howell had makeable birdie tries at both the par-3 17th and the closing hole, but could not get either to fall.
Still, Howell is in the hunt for his second PGA TOUR victory. His only other trip to the winner's circle came at the 2002 Michelob Championship at Kingsmill, a tournament that is now defunct.
Much was expected of Howell when he broke on tour, but it hasn't panned out. The 27-year-old seems poised to return to winning.
'I've been through my fair share of swing changes and stuff like that,' admitted Howell. 'I've had an iffy year with the stats, but this week it's been a bit better.'
Curtis, playing in the last group, collected his first birdie at the par-5 fifth. He rolled in a 35-foot birdie putt at the sixth to reach 11 under par for the championship.
He ran into trouble at the par-4 10th when he drove into the right rough. Curtis could not get up and down from 7 feet, but with the fluctuating leaderboard on Saturday, he was never that far out of the lead.
At the par-3 12th, Curtis drained a 25-footer for birdie to get back to minus-11. He parred his next three, but tapped in a short birdie putt at 16 to match Howell in first.
Curtis hit a horrible 9-iron well short of the putting surface at 17. He pitched 8 feet short of the flag, then converted the par save. Curtis had a good look at birdie on 18, but his 12-footer dove left.
Briny Baird (67), Brett Quigley (68), Steve Stricker (70), first-round leader Nicholas Thompson (71) and this year's Nissan Open winner Rory Sabbatini (70) are knotted in ninth place at minus-9.
Charles Warren, Michael Allen, Will MacKenzie. Jason Bohn and Jeff Gove are also in the mix after three rounds at 8-under-par 208.
Defending champion Jason Gore shot a 2-under 70 and is part of a group tied for 43rd at minus-3.
None of the three U.S. Ryder Cup players who made the cut, made a move on Saturday. David Toms shot a 70 and is tied for 52nd at 2-under par, Chris DiMarco also carded a 70 on Saturday and trails Toms by one shot. Brett Wetterich only managed a 2-over 74 and is alone in 78th at plus-3.