"I played great today - ball striking was on point today and I wasn't feeling worried about one single shot out there - I felt like I could pull off any shot," said Lee.
Lee rolled in 94 feet of birdie putts as part of his seven-birdie round, the best of the day being a 27-footer on the 18th to put him on top of the leaderboard.
"My putting stats have been getting better, starting from a couple of months ago. Besides missing a three-footer birdie putt on number two, everything else was good," said Lee, who ranks 67th on the Tour in putts per round.
The top of the leaderboard is congested by several notable names. Kevin Kisner, Scott Piercy and former major winner Webb Simpson are alongside Lee at six-under, but the big threats for the title sit just further back.
Paul Casey, Masters champion Sergio Garcia and young star Jon Rahm are just one shot off the pace, while Jordan Spieth lurks at two-under.
For his part, Lee is excited to get back with a chance to win on the weekend.
"I haven't been in contention for so long, I felt like my game had just gone away for a while. I had a great finish last week, that kind of gave me the motivation to carry the great rounds over."
Elsewhere, fellow Kiwi Ryan Fox missed the cut by four shots at the prestigious BMW Championship on the European Tour.
