The Briton led the way as just 0.283 seconds separated the top three teams.
“The gap closed up a little bit, but that’s exciting anyway,” he said.
“It’s more challenging for me to eke out more from the car, discover whether I have lost something or they have all gained, but I enjoyed driving.”
Hamilton was 0.127secs clear of Red Bull’s Max Verstappen, although the world champion looked as if he had more potential had he not lost time on his quickest lap.
The world champion’s team-mate Valtteri Bottas was third, from the Ferrari of Kimi Raikkonen.
Rain is expected across the weekend for what would be only the fourth wet Australian Grand Prix in 34 years of the event.