The Monegasque driver was the pick of the field with a best lap of 1minute 11.684seconds, just 0.112s quicker than Sainz in his first season with the team.
Lewis Hamilton proved the best of the rest a further quarter of a second back from Sainz.
Although it is notoriously difficult to read too much into practice times, both Ferraris were consistently quick on the street circuit ahead of Sunday’s race throughout the two practice runs.
In the earlier morning run, Sainz had been second fastest behind Sergio Perez although the Red Bull driver had been one of the few drivers on the soft tyres, while the entire field were on the softs in the second session.
That latter session, though, was brought to a premature end with a few minutes remaining because of Mick Schumacher’s stricken Haas blocking the circuit.
Of Ferrari’s shock pace, Max Verstappen, who struggled for track position when the soft tyres were at their optimum, said: “I’m surprised how competitive Ferrari is. They’re doing very well and we’re very weak. A lot of things need to change. The gap they have around here is big.”