The Stirling player, who played all but six minutes of the first Test last Saturday after replacing the injured Gordon Bulloch, held off the challenge of Steve Brotherstone, who is named on the bench.
McKenzie's selection reflects the need for as much experience as possible in the team and the belief that the hooker's shortcomings at the throw- in can be rectified.
"We have been working with McKenzie and equally so Brotherstone to make sure each is equally adept. The throws have to be accurate," said the Scotland coach, Jim Telfer.
Scotland have fitness worries over the wing Derrick Lee, who picked up an injury in the midweek side's 27-22 defeat by Queensland in Brisbane on Wednesday. Lee has bruising on his Achilles tendon and did not take part in training yesterday.
If Lee is ruled out then the likelihood is that Craig Joiner will play on the right wing and Hugh Gilmour, who put in an impressive performance at full-back against Queensland and who is unlucky not to be named in the squad of 22, will be promoted to the replacements' bench.
Ireland will field an unchanged side for Saturday's second Test in Pretoria. Ireland lost the first Test 37-13 in Bloemfontein last Saturday, but surprised the Springboks with that performance.
SCOTLAND (v Australia, second Test, Ballymore, Saturday): G Metcalfe; D Lee, C Murray, R Shepherd, S Longstaff; G Townsend, B Redpath; D Hilton, K McKenzie, M Proudfoot, S Murray, S Grimes, R Wainwright (capt), E Peters, G Simpson. Replacements: C Joiner, D Hodge, G Burns, A Roxburgh, S Campbell, G McIlwham, S Brotherstone.
IRELAND (v South Africa, second Test, Pretoria, Saturday): C O'Shea; J Bishop, M McCall, K Maggs, D Hickie; E Elwood, C McGuinness; V Costello, A Ward, D O'Cuinneagain, M O'Kelly, P Johns (capt), P Wallace, K Wood, J Fitzpatrick.
l London Scottish have secured a ground-sharing arrangement with Harlequins next season. Scottish, newly promoted to Premiership One, will play at The Stoop for an initial three-year period. The Exiles' decision means that there will be no top-flight rugby at Richmond Athletic Ground next term.Reuse content