The Socceroos needed a late strike to kick off their Asian Zone Group D campaign with a hardlky deserved 2-1 victory at home to Thailand last week but were much more convincing in Dammam.
Kennedy was the hero for the visitors, bagging the opener with a header on 40 minutes before adding a second with a well-placed shot 11 minutes into the second half.
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The Saudis, coached by former Barcelona boss Frank Rijkaard, were hugely unconvincing throughout but managed to pull one back from the penalty spot after 65 minutes, Nassir Al Shamrani tucking the ball home.
But Holger Osieck's Australians, who won despite keeping star man Tim Cahill on the bench until the 86th minute, wrapped up the points when defender Luke Wilkshire slotted home a penalty 13 minutes from time.
It was awarded after Kennedy was fouled in the box during a cornerkick action.
Elsewhere in Group D, Thailand ran out 3-0 winners at home to Oman.
Sompong Soleb fired the host ahead in the 35th minute and Teerasil Dangda made it 2-0 six minutes later. Rashid al Farsi's late own goal compounded Oman's misery.
