As has been the case since the British GP, the opening 45-minute session of the weekend does not count towards the qualifying groups for Saturday.
Run under dry conditions, Zarco fired in a 1m29.838s after switching to a fresh medium rear tyre to end first practice 0.399 seconds clear of the field.
He bested 2021 world champion Quartararo and the Aprilia of Maverick Vinales.
Vinales set the early pace on his RS-GP with a 1m31.751s before Ducati’s Enea Bastianini edged ahead with a 1m30.852s inside the first six minutes of the session.
A subsequent 1m30.270s re-established Vinales at the top of the order, which stood as the benchmark for around the next eight minutes.
Continuing to run the new aerodynamic package he raced at the British GP, Yamaha’s Quartararo deposed his former team-mate with a 1m30.237s as the clock ticked into the final half an hour.
Quartararo, who has topped just two warm-up sessions across 2023 so far, looked on course to end FP1 fastest of all as the chequered flag neared.
But a final flyer for Zarco on his Pramac-run Ducati ensured he saw out opening practice on top.
Behind the top three came Gresini’s Alex Marquez on a 1m30.286s. He was forced to park up early on in the session due to an apparent front fork issue, which led to smoke bellowing out of his bike every time he touched the front brake.
Source: Autosport