As fellow Australians Min Woo Lee and Jason Day slipped down the leaderboard on moving day, Smith surged to within two shots of the frontrunners with a third-round two-under-par 68.
After missing the cut at the past six majors, the 2022 British Open champion and one-time world No.2 last week made the gut-wrenching decision to part ways with his lifelong coach Grant Field.
Field had been in Smith's corner since he was a Brisbane junior but, after missing the cut again at last month's Masters, the 32-year-old turned to Claude Harmon III, the son of swing guru Butch Harmon.
"It was a terrible, terrible conversation to have," Smith told todaysgolfer.com of the decision to split with Field.
"I've been seeing Grant since I was like nine years old, and he's a really good friend as well, so it was tough."
But the change-up has paid immediate dividends this week at Aronimink Golf Club in Pennsylvania.
Smith only found six fairways on Saturday but, as he does, the short-game wizard scrambled brilliantly and only needed 28 putts for the round.
He enjoyed a spectacular mid-round burst of four birdies in five holes either side of the turn but cursed himself for lipping out from seven foot with the chance to pull to within one stroke of the lead on the par-3 14th.
Smith, though, held his cool to par his last four holes to give himself a winning shot on championship Sunday.
Lee was fighting desperately to also stay in the mix late in his rollercoaster third round.
He offset back-to-back bogeys on holes three and four with successive birdies on six and seven, where he drove the green at the 397-yard par 4.
But just as he moved back to within a shot of the lead, Lee made a complete mess of the par-5 ninth.
Going from rough to rough and then three-putting, he racked up a disastrous double-bogey seven on a hole playing the second easiest of the week.
Deflated, Lee missed a short birdie putt on the next hole, then dropped another shot on 13 before making birdie on 14 to move back into red figures at one under for the championship.
From a position of promise, Day misfired to lose all hope of having his named etched on the famous Wanamaker Trophy for a second time.
Like Lee, the 2015 champion rebounded from two early bogeys with consecutive birdies only to also post a dreaded double on the treacherous 10th hole to slip from one under to over par.
Playing catch-up, Day dropped three more shots in his last four holes for a 75 to wind up at four over - a distant eight strokes adrift of the pacesetters.
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