Perez was just 0.004 seconds ahead of Ferrari’s Charles Leclerc, with the Mexican’s teammate Max Verstappen third at Interlagos as the drivers grappled with a slippery track.
Carlos Sainz was fourth fastest overall 0.186 seconds behind Verstappen, with the Mercedes pair of Lewis Hamilton and George Russell close behind.
Sebastian Vettel was the best of the rest for Aston Martin in seventh, ahead of Mick Schumacher, Valtteri Bottas, and Pierre Gasly.
More wet weather is expected across the weekend, with downpours and potential thunderstorms forecast for both the Sprint Race and Grand Prix.
The conditions and the prospect of a mixed grid from the sprint race mean that we could see a hotly contested race on Sunday, as Mercedes and Ferrari look to close the gap to Verstappen and Red Bull at the top with an eye to 2023.