Campbell, former world No.1 Jon Rahm and US star Bryson DeChambeau are 12 under at the Grange on Saturday.
Englishman Tyrell Hatton, on a hot streak with five birdies in a six-hole stretch, is also 11 under, with Anthony Kim and Brandon Grace at 10 under.
Campbell, a 34-year-old from Queenstown, birdied the par-4 4th as he chases the biggest cheque of his career - Adelaide's champion collects $US4 million ($A6.2 million).
Australia's Cam Smith was making ground, three birdies in four holes taking him to eight under, equal with compatriot Lucas Herbert.
Fellow Australian Marc Leishman, who was co-leader with DeChambeau at six under after the opening round, is seven under.
And Elvis Smylie, who won on his LIV debut last weekend in Saudi Arabia, is four under, with the combined Australian efforts putting Smith's Ripper GC four strokes shy of Rahm's Legion XIII in the team standings.