Piastri's fellow title contenders Lando Norris -- second behind Mercedes' George Russell -- and third-quickest Max Verstappen both finished clear of the Australian on Saturday in a session marred by a crash for Lewis Hamilton in his Ferrari.
Russell denied McLaren's championship leader Norris a sweep of fastest times in all three practice sessions by just 0.004 seconds but things are looking good for the McLaren driver.
He leads Red Bull's four-time world champion Verstappen by 12 points with McLaren teammate Piastri a further four adrift and the 26-year-old, on a track where overtaking is difficult, is looking well set for the Sunday podium finish that would guarantee him the title.
Verstappen was third, just 0.124 off Russell's session-leading best lap of 1min 23.334sec, with Piastri fifth, 0.259sec slower than the pacesetter. Aston Martin's Fernando Alonso finished fourth.
The main drama of the morning came when Hamilton had a big spin at turn nine before careering into the tyre wall halfway through the session.
"Something buckled at the front and snapped the rear," reported the Briton, who's had a miserable first season with Ferrari, over the team radio.
Norris had earlier also had to swerve to avoid Yuki Tsunoda's dawdling Red Bull while the Japanese was also involved in a pitlane collision with Mercedes' Kimi Antonelli as both cars suffered damage.
Mercedes released the Italian rookie from the garage straight into Tsunoda's path, with stewards investigating.
Verstappen was again not happy with his Red Bull, complaining about his car jumping. "I can't keep my feet on the pedals," he said over the radio.Â
With agencies
