The Australian is tied for 11th, four shots behind leader Sam Burns, after two rounds.
Lee carded a six-under-par 66 at the Pete Dye Stadium course, following his seven-under 65 at the Nicklaus course in the opening round.
Despite being 13 under, Lee says he's yet to hit his straps.
"I made the most out of the last two days," he said.
"I'm a little tired in my legs ... I don't feel 100 per cent fresh and the swing doesn't feel amazing too.
"But I managed to grit it out a little bit and make some good up-and-downs when I needed to.
"I feel like I've done really well, pat on the back actually."
Fellow Australian Cam Davis is tied for 26th at 11 under after shooting a seven-under 65 at the Peter Dye course.
Former world No.1 Jason Day is 10 under after rounds of 68 and 66.
Australia's Harrison Endicott (70, 68) is six under with countryman Aaron Baddeley at four under after recovering from his opening-round 74 with a 66 on Friday.
American Burns fired a career-low 61 at the Nicklaus course on Friday to lead the tournament at 17 under, one shot clear of compatriot Michael Kim.
Reigning US Amateur champion Nick Dunlap is at 15 under, alongside South Korea's K.H. Lee.
Dunlap is seeking to become only the eighth amateur to win on the US PGA Tour since 1945 and the first since Phil Mickelson in 1991.
But Burns is the man to catch in the tournament staged at three courses and with a 54-hole cut after scorching the Nicklaus course with seven birdies and two eagles.
"Obviously everybody is shooting some good numbers so I'm just trying to keep pace and hit as many quality shots and get as many looks as possible," Burns said.
"The greens are really good ... so I think it comes down to being able to make some key putts."
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