Lewis did his damage on the Magnolia Course at Walt Disney World Resort. Magnolia and the Palm Course are being used for the first two rounds, before the final two rounds will be contested on the Magnolia Course.
Scott Hend, Mark Hensby and John Huston share second place at 8-under-par 64. Stephen Ames, Briny Baird and two-time Masters Champion Jose Maria Olazabal are one stroke further back at minus-7.
World No. 1 and defending champion Vijay Singh shares eighth place with eight other players at 6-under-par 66.
Lewis opened his round on the back nine and two-putted for birdie at the par-5 10th to quickly move into red figures. He stuck a sand-wedge within a foot of the cup at the next to make it two straight.
The two-time winner on the PGA Tour made it three straight as he ran home a 25-foot birdie putt at the 12th. Lewis knocked a pitching-wedge to 6 feet and he drained that putt to open with four consecutive birdies.
Lewis stumbled to a bogey at the 15th, but bounced right back with a 6-foot birdie putt at the next. He parred the next two holes to make the turn at minus-4.
The 44-year-old Lewis made back-to-back birdie putts from the first, both from within 10 feet, to move to minus-6. He got up-and-down for birdie at the par-5 fourth.
Lewis came right back with a birdie at the next and made it three straight as he drained an 18-footer for birdie at six. Lewis drained the 11th birdie of his round at the eighth when he rolled in a 25-footer to get to minus-10.
'I played well and I putted really well, though I missed a couple out there, but I made most of them, so I'm pretty happy,' Lewis said. 'This year has been kind of an off year, and I've just been working on executing shots and trying to just get more proficient, and hopefully it's paying off.'
Singh played the back nine of the Palm Course first. He converted back-to-back birdies from the par-4 13th and cruised around the turn with four straight pars.
The Fijian moved to minus-four with birdies at the first and third. Singh closed his round with birdies at the seventh and ninth to get within four shots of the lead.
Hend birdied the 10th on the Magnolia Course, then ran off four straight birdies from the 13th. The 31-year-old birdied Nos. 2 and 3 and picked up an eagle at the fourth to move to minus-9. Hend dropped shots with bogeys at the fifth and seventh, but shares second place at minus-8 thanks to a birdie on the eighth.
Hensby also played the back nine of the Palm first. He picked up a pair of birdies on his opening nine. On the front side, Hensby converted birdies at one and two, before running off three consecutive birdies from the fifth. He grabbed a share of second place with a birdie at the ninth.
Huston played the front side of Magnolia first. He birdied No. 1, but faltered to a bogey at the next. The seven-time winner on the PGA Tour then birdied the next six holes to make the turn at 6 under.
Huston tripped to another bogey at the 10th. He bounced right back with a birdie at the 11th. Huston joined Hensby and Hend in share of second with birdies at the 16th and 18th.
Singh is joined at minus-6 by Bart Bryant, Joey Sindelar, Kirk Triplett, Tommy Armour III, Ben Curtis, Dudley Hart, Skip Kendall and Tom Lehman.