Scott rolled back the years with five birdies and an eagle three at the 18th for an unblemished seven-under 63 to join overnight leader David Micheluzzi on eight-under 134.
In the adjoining women's tournament held on the same sandbelt courses at Kingston Heath and Victoria Golf Club, Australia's Hannah Green swept into the lead after a six-under 66.
In contrast to 2014 Masters champion Scott's brilliant round, world number three and British Open champion Smith stuttered to a one-over 73 to just scrape into the weekend rounds in a tie for 60th on two-over 144.
"I'm here to win the tournament this week and I can turn things around quick, I have that experience as well and it did today," world number 36 Scott said.
"I hit some much better shots today. I mean, I'd be lying if I said I'm 100 percent confident with exactly where it's going, but I had a better idea today.
"You have to let go of some of the inhibitions or the fear of going offline and just swing the club."
Smith said his mind was "foggy" and his second round was "pretty rubbish" as the major tournament drawcard looked for much of the day that he would sit out the weekend.
Smith's opening two rounds included just six birdies, nine bogeys and 21 pars.
"I was just really uncomfortable all day, kind of similar to yesterday, just couldn't quite hit the ball out the middle of the club face for some reason or another," Smith said.
"My mind was a little bit foggy, obviously a little bit tired as well. Last week had been such a big week (winning the Australian PGA title), so yeah, just pretty disappointing. That was pretty rubbish out there today."
Green, the 2019 Women's PGA champion, reeled off an eagle and five birdies to lead the women's event by two shots from South Korea's Jiyai Shin.
"I kind of expected all of the good players to come out on top, especially playing here at Victoria," world number 20 Green said.
"Even though I shot a lower score than in the first round at Kingston Heath, I thought this was a difficult golf course... we'll just see how the conditions pan out come the weekend."
Reigning Women's British Open champion Ashleigh Buhai of South Africa carved out a bogey-free round at Kingston Heath to get to seven-under, four strokes off the lead.
Australia's world number four Minjee Lee moved up to sixth after a three-under 70.
"I played pretty solid so hopefully I can play better at Victoria come the weekend," she said.
