The Briton, one point clear of the Australian with four rounds remaining, including two Saturday sprints, lapped the Interlagos circuit with a best time of one minute 09.975 seconds on medium tyres.
Piastri, who lost the lead to Norris in Mexico last month, ended up 0.023 seconds slower after his teammate set the best time with his last flying lap of the session.
McLaren, who have already won the constructors' title for a second year in a row, again looked significantly faster than the rest.
Drivers get only one practice due to it being a sprint weekend, the fifth of six this season, with the usual second practice becoming qualifying for Saturday's 100km race.
Sauber's Nico Hulkenberg was third fastest, 0.619 off the pace, with Aston Martin's Fernando Alonso fourth.
Brazilian rookie Gabriel Bortoleto, Hulkenberg's teammate preparing for a first home race, was fifth on the timesheets with Mercedes' George Russell sixth and Alpine's Pierre Gasly a surprising seventh.
Williams' Carlos Sainz, who missed Thursday's media day due to feeling unwell, was eighth ahead of Racing Bulls' Isack Hadjar and Mercedes' Kimi Antonelli.
Ferrari's Charles Leclerc was 18th and Lewis Hamilton, a three-time winner in Brazil, 19th with Red Bull's Max Verstappen -- the closest title rival to the McLaren pair -- only 17th but without any running on the medium tyre.
Both Ferrari drivers stuck with the hard tyres for the session, Hamilton spinning at turn 11 in the final seconds.
Verstappen, 36 points off the lead, won from 17th in Brazil last year.
Red Bull's Yuki Tsunoda spun on the kerb and thumped into the barriers at turn four early in the session, continuing back to the pits with damage to the front and rear wings.
The Japanese returned after repairs, with 25 minutes remaining.
"You never want to start the session like that. These things happen," team boss Laurent Mekies told Sky Sports television.
