Home hero Piastri edges Antonelli in second Australian GP practice
The Australian sent his home crowd into a frenzy by blasting round the Albert Park circuit in one minute 19.729secs on soft tyres, 0.214 clear of Antonelli.
Antonelli's teammate, pre-season favourite George Russell, came third, a fraction clear of Ferrari's seven-time world champion Lewis Hamilton.
Charles Leclerc, in the other Ferrari, was fifth with four-time world champion Max Verstappen sixth after spending half the session in the garage having stalled his Red Bull.
McLaren world champion Lando Norris clawed his way to seventh, more than one second off the pace, after managing only seven laps in first practice due to gearbox issues.
Racing Bulls' impressive rookie Arvid Lindblad banked an eye-opening eighth, a place ahead of Isack Hadjar -- the man he replaced and who is now Verstappen's teammate.
It was the first proper test of far-reaching new engine and chassis rules with the hybrid power units now 50 percent traditional combustion and 50 percent electric.
With a finite amount of energy available, drivers had to carefully manage their batteries on each lap, working out when to deploy while building it up back through braking.
The challenge of Albert Park is its long sweeping straights, which deplete batteries, and relatively few twisty turns to brake and charge it up again.
There have also been changes to the aerodynamics of the cars, which are lighter and smaller.
On a perfect Melbourne afternoon, Nico Hulkenberg led them out, but it was Hamilton who set the opening time.
Verstappen had an inauspicious start, stalling in the pit lane, while Russell clipped Lindblad on his way out and needed a new nose.
Verstappen's car was wheeled back into the garage, apparently stuck in gear, where he stayed for almost half an hour.
The drivers started on a mix of medium and hard tyres and Russell soon upstaged Hamilton as they jockeyed for places.
At the halfway mark it was Italy's Antonelli, Russell, Hamilton and Piastri.
Russell locked up and hit the gravel at Turn 3 as he pushed hard, with Hamilton doing the same, but they both kept enough momentum to get back on track.
Piastri blasted to the top of the timesheets on soft tyres with 25 minutes left as Verstappen began climbing the leaderboard.
But the Dutchman was trying too hard and careered into the gravel at Turn 10 with debris flying off his car, ending his day early.
Fernando Alonso clocked 18 laps and Lance Stroll 13 as the troubled Aston Martins battle extreme vibration caused by the new Honda power unit.
Newcomers Cadillac -- the 11th team on the grid -- also struggled with Valtteri Bottas 19th and Sergio Perez last.
In first practice, Leclerc outpaced Hamilton by nearly half a second with Verstappen and Hadjar third and fourth.