England were bidding to avoid a record-equalling 10th consecutive defeat, which has left Cook's position in jeopardy.
The 29-year-old revealed after the seven-wicket defeat in Sydney last Sunday that he was considering his position, with a review into the troubled tour to be conducted after he flies home early next week.
In his first public comments since then, Cook suggested he was determined to remain in charge adding that his comments after the series-conceding defeat at the SCG had come at an "emotional time".
Cook made his comments at the toss in Perth, which he lost to see his side sent in to bat on a cloudy and windy morning.
Australia named their starting XI, 24 hours earlier, with skipper Michael Clarke, David Warner, Brad Haddin and Shane Watson all rested.
George Bailey recovered from a hip injury to take over as captain with fellow Ashes winners Mitchell Johnson and Steve Smith coming in alongside Matthew Wade.