Stephen Hoiles will continue to deputise for injured skipper Dave Dennis on the blindside so the versatile Potgeiter shifts into lock.
Horne will mark Brumbies flyer Henry Speight who bewitched the Chiefs last weekend and has been added to the Wallabies squad for the Rugby Championship in place of Nick Cummins who is heading to Japan.
The Brumbies were without four Wallabies when they were last dusted by the Waratahs but have them all back on duty for Saturday's duel.
Assistant coach Laurie Fisher has put the acid on his loosehead prop Scott Sio to set the physical standards after the team's lacklustre performance in their last meeting.
Versatile Wallabies loose forward Scott Fardy, who turns out at lock alongside another international squad member Sam Carter, said the Brumbies were determined to overcome their outsiders' rating.
"They've [Waratahs] been excellent this year, they've won eight in a row and they're at home, so they're definitely favourites this week."
The Brumbies tuned up for the semifinal by beating the Chiefs in the quarter-final when they pushed out to a significant lead and held out the erratic visitors' late surge.
Meanwhile the Tahs had the week off to repair some bodies and their lineout which melted in their recent game with the Reds. They also lost the turnover battle that night.
Those faults would have been top of Cheika's corrections manual as he continued to deliver the mantra about power and attack which have taken the Tahs to the brink of a historic Super 15 title.