US star DeChambeau and former world No.1 Rahm are co-leaders at 19 under, five strokes ahead of the pack after three rounds at the Grange.
"I hope it's a banger," Rahm said of their duel on Sunday.
"It should, in theory, turn into a two-man race if we play as good as we have this week.
"In that essence, it will have that feel - Bryson and I going at each other.
"But I wouldn't put it past anybody to go out and shoot 10-under tomorrow."
The drawcard duo hold a massive break from next-best, American Anthony Kim (14 under).
Australians Cam Smith and Lucas Herbert are 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 before a raucous home crowd.
"A guy shouted out to me on the 17th tee, he said: 'Fire up'," Smith said.
"I'm like: 'I don't think I can fire up anymore, if I fired up any more  my head would just explode'.
"I was really out there on a mission."
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.
Rahm followed his nine-under 63 on Friday with bogeys on his initial two holes.
But he rallied with six birdies and, on the 18th, holed a wedge from 62 metres for eagle.
"Executed it pretty well," said the understated Rahm.
"I'm hoping to hit it close but obviously ended up with the grand prize on that one."
Rahm's playing partner DeChambeau produced an astonishing stretch of nine birdies in 11 holes.
"We're two fierce competitors," DeChambeau said.
"It's going to be a fun battle tomorrow."
The American's 64 - he dropped a shot with bogey on the 17th - 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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