Lewis is tied at 7-under-par with Andrew McLardy, who birdied the 18th to tie for the top spot.
McLardy, a 27-year-old Zimbabwean, is a rookie on tour after finishing tied for fifth at the 2000 Qualifying Tournament.
Jerry Smith, Paul Gow and Stephen Allan are tied for third place at 6-under. Allan was the 2000 PGA Tour Q-School medallist.
Its been two years since Lewis last tasted victory, doing so at this very event. This year the 41-year-old has made 16 of 19 cuts; however, he's yet to record a top-10 finish.
Thursdays 64 was Lewis lowest round of the year. He started with three birdies over his first five holes, and then did the same on the back nine. He completed his scoring with his seventh birdie of the day at the par-5 17th.
Lewis had a strong showing in this years U.S. Open. He was a co-leader through two rounds, only to shoot 77-75 on the weekend to finish in a tie for 30th.
Gow is fresh off his runner-up finish in last weeks B.C. Open. The man who beat him in a playoff, Jeff Sluman, was 3-under through 17 holes Thursday, but double bogeyed the final hole to finish at minus-1.
Full-field scores from the John Deere Classic