Pedro Acosta takes the first top spot of the weekend with a 1:26.688 lap in Brazil.
The Spanish rider edged out Jack Miller by 0.087 and Marco Bezzecchi by 0.230.
What happened in the first session?
The first session was delayed due to rain, but eventually got underway with riders starting on wets.
The track conditions kept changing as it dried out, with Marc Marquez leading the way early on.
How did the session unfold?
As the track dried out, riders started to switch to slicks, with Jack Miller being the first to do so.
The timesheets lit up in the final ten minutes, with Pedro Acosta taking the top spot.
Who were the top performers?
Pedro Acosta was followed by Jack Miller and Marco Bezzecchi, with Marc Marquez demoted to fourth.
Fermin Aldeguer had a notable performance, finishing eighth despite returning from a broken leg.
The session saw no crashes, with only a few moments of concern, including a run off for Joan Mir.
Pedro Acosta's lap time of 1:26.688 was the fastest of the session, set on March 20, 2026.
The riders will be back on track for the next practice session, which will decide the direct Q2 entrants.
The session will start at 16:00 (UTC-3) and will be crucial in determining the grid for the Brazilian GP.