Replacing injured vice-captain Ashwell Prince, Duminy made his Test debut against Australia at the WACA in Perth on 17 December 2008, scoring 50 not out in the second innings and putting on an unbroken century partnership with AB de Villiers. His performance was lauded by numerous critics, including Peter Roebuck. In the next Test match Duminy combined with the tailenders to score his maiden Test century, making 166 runs. South Africa were more than 200 runs in arrears when they lost their seventh wicket in the first innings. In the process, he and Dale Steyn put on 180 and surpassed Graeme and Peter Pollock's South African ninth wicket partnership record against Australia. South Africa ended with a 62-run lead and converted it into a nine-wicket win. This sealed the series, the first time that South Africa had won a Test series in Australia, and Australia's first home Test series loss in 16 years. He also took his first Test wicket in the 3rd Test of the tour.