US star DeChambeau and former world No.1 Rahm share the lead after three rounds at the Grange.
The major winners enter Sunday's final round locked at 19 under, with American Anthony Kim next-best at 14 under.Â
Australians Cam Smith and Lucas Herbert are both tied fourth at 13 under, alongside American Peter Uihlein and Englishman Tyrell Hatton.
Herbert enjoyed a hot streak of six consecutive birdies - he shot nine in a round punctuated by four bogeys to card a five-under 67.
And countryman Smith made a big move, firing eight birdies in a bogey-free 64.
Compatriots Marc Leishman (eight under) and Elvis Smylie (six under) have Smith's all-Aussie Ripper GC placed second in the team standings, four shots behind Rahm's Legion XIII.
Spain's former world No.1 followed his nine-under 63 on Friday with bogeys on his initial two holes.
And while Rahm rallied with six birdies, his playing partner DeChambeau produced an astonishing stretch of nine birdies in 11 holes.
The American's 64 followed rounds of 66 and 67 at the sandbelt course in Adelaide's beachside west.
DeChambeau and Rahm played with unheralded New Zealander Ben Campbell, a 34-year-old from Queenstown who lost traction with an even-par 72 and is 12 under.
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