For Curtis, this was his second win of the year after capturing the Booz Allen Classic in the summer. This win makes three to go along with his victory at the British Open three years ago.
'This feels great,' acknowledged Curtis, who collected $828,000 for the win.
Howell, who shared the lead with Curtis after Saturday's third round, only managed an even-par 72 to finish at minus-12. Brett Quigley posted a 2-under 70 and finished alone in third place at 11-under-par 277.
Sunday, much like Saturday, featured quite a few lead changes with little stability at the top.
Curtis stumbled with a bogey at the par-4 second, but a 13-foot birdie putt at the fourth and a birdie putt from a similar distance at five moved him one clear of the field at minus-13.
When Howell, who tallied one birdie and one bogey through seven holes, kicked in a short birdie putt at the eighth, the pair was tied. Curtis dropped a shot at the ninth to fall one behind, but Howell bogeyed 10 to fall back into a tie for the lead.
Curtis took the lead for good with a 7-foot birdie putt at the 12th. Things looked like they were falling apart for the British Open winner, after he missed the green at 13. He chipped close to save par, then did the same at 14 when he sank a 10-footer for par.
Curtis was still one ahead of Howell when the two reached the 15th green. Curtis drove into a fairway bunker, but no matter as he knocked his approach to 13 feet. Howell got on the green in two, but hit a horrible birdie putt from 50 feet. Curtis drained his birdie putt, but Howell missed his 10-footer for par.
The two-shot swing moved Curtis three ahead. Howell birdied 16 and Curtis took the conservative approach at the par-5 hole by laying up with his second. His third stopped close to 50 feet from the stick, but he ran home the long birdie putt to maintain his three-shot lead.
At the par-3 17th, Curtis came up short of the flag and lagged his long birdie putt 4 feet short. He missed that par putt to make the closing hole more interesting.
Curtis found the fairway off the tee at 18, then hit a 6-iron 18 feet from the hole. Howell could not even manage a birdie, so Curtis knocked his birdie putt to tap-in range. Curtis kicked in the short putt for the victory.
For Curtis, the 2006 season has been a validation of sorts. Most perceived him as a fluke champion when he outlasted the field at Royal St. George's, but with a multiple-win season, that talked has died down.
'All the hard work you go through, it's just nice to have a good year and play solid for 24 weeks out of the year,' said Curtis.
Robert Garrigus held the lead during the final round, but back-to-back bogeys to close his round dropped him down the leaderboard. He finished with a 1-over 73 and tied for fourth place with Ted Purdy, who shot a 5-under 67 on Sunday. The pair came in at 10-under-par 278.
Kent Jones (67), Charles Warren (71) and Ryan Moore (73) tied for sixth place at minus-9.
Jeff Overton (69), Steve Stricker (73), Briny Baird (73), Greg Owen (75) and Hunter Mahan (75) shared ninth place at 8-under-par 280.