Lando Norris led Oscar Piastri to a McLaren one-two in first practice at the Azerbaijan Grand Prix.
The familiar look to the timesheets, with Ferrari's Charles Leclerc and Mercedes' George Russell third and fourth, belied an incident-packed hour.
A red flag because of a loose kerb interrupted proceedings for about 20 minutes, and limited the disadvantage that an engine problem could have inflicted on Piastri.
Lewis Hamilton clipped the wall in his Ferrari, damaging his front wing and giving himself a front-left puncture, on his way to 12th fastest time.
The delay was caused when a strip of rubber came loose underneath the kerb at Turn 16, the last corner on to the long pit straight.
The session was stopped while officials tried to resolve the problem, giving McLaren time to fix a power-unit issue that that had been discovered on Piastri's car on his first lap out of the pits.