The Ferraris of Charles Leclerc and Carlos Sainz set the first somewhat representative times on the board in the opening minutes, with Leclerc's 1m19.283s heading his team-mate by 0.166s.
They were soon demoted by Mercedes duo George Russell and Lewis Hamilton, Russell leading with a 1m18.644s while the Red Bulls sat out the opening third of the session.
Gasly suffered a spin on his mediums run as he entered the Foro Sol arena, with an off-track excursion by Yuki Tsunoda in the same corner further proof that grip still came at a premium.
Season dominator Max Verstappen entered the fray after 22 minutes and split the two Mercedes cars with his first flyer, a 1.18.717s less than a tenth behind Russell.
His Mexican Red Bull team-mate Sergio Perez, who was received with goal-like celebrations by the home crowd every time he passed through the iconic stadium section, opening his account with the sixth-fastest time.
AlphaTauri's Daniel Ricciardo then demoted Perez as he took fourth on medium tyres, six-tenths shy of Russell. The Australian benefitted from a generous tow by team-mate Tsunoda, foreshadowing the prospect of similar team tactics in qualifying.
Right before the halfway mark Verstappen's second effort of 1m18.429s was enough to knock Russell off the top spot by two-tenths, with Perez moving to third, another tenth in arrears.
Source: Autosport