McMahon earns spot on the bench
Cheika, who had already named his starting side for the third leg of Australia's Grand Slam bid, had left one bench spot open in his matchday 23.
But he has now opted for a five-three split between forwards and backs, with back row McMahon joining playmaker Quade Cooper and Sefanaia Naivalu among the replacements, after Lopeti Timani was dropped from the matchday squad.
McMahon will be looking to add to his 13 Test caps while Naivalu starred on the wing during a 25-23 win over France in Paris last weekend.
Saturday's match in Dublin will see Australia captain Stephen Moore earn his 116th cap, joining Adam Ashley-Cooper and Nathan Sharpe as the second most-capped Wallaby in history.
Australia will be chasing a fourth successive Test victory, in what would be their best sequence since they won seven in a row on their way to last year's World Cup final.
Ireland and Australia have each won three of the last seven Tests between the two countries, with the 2009 encounter at Lansdowne Road drawn.
Australia: 15 Israel Folau, 14 Dane Haylett-Petty, 13 Tevita Kuridrani, 12 Reece Hodge, 11 Henry Speight, 10 Bernard Foley, 9 Will Genia, 8 David Pocock, 7 Michael Hooper, 6 Dean Mumm, 5 Rob Simmons, 4 Rory Arnold, 3 Sekope Kepu, 2 Stephen Moore (captain), 1 Scott Sio.
Replacements: 16 Tolu Latu, 17 James Slipper, 18 Allan Alaalatoa, 19 Kane Douglas, 20 Sean McMahon, 21 Nick Phipps, 22 Quade Cooper, 23 Sefanaia Naivalu.
Agence France-Presse
