The Leonardo DiCaprio thriller took in $3.15 million to narrowly edge out Sylvester Stallone's latest action movie The Expendables to the top spot.
Step Up 3D falls a place to number three, comic adaptation Scott Pilgrim Vs. The World debuts at four and action-comedy Killers is at five.
Elsewhere, Roman Polanski's The Ghost Writer climbs up to number six after charting in the top ten in pre-release screenings last week, while Tom Cruise and Cameron Diaz's Knight And Day drops sharply to number eight.
The box office top ten in full (figures in Australian dollars):
1. (1) Inception - $3,157,091
2. (-) The Expendables - $3,141,387
3. (2) Step Up 3D - $2,11,026
4. (-) Scott Pilgrim Vs. The World - $943,258
5. (3) Killers - $649,066
6. (9) The Ghost Writer - $595,031
7. (5) Toy Story 3 - $362.816
8. (4) Knight And Day - $310,407
9. (6) The Twilight Saga: Eclipse - $214,259
10. (7) The Karate Kid - $162,843