More than half the session was lost due to a lengthy stoppage while barrier repair works were carried out following a heavy crash for Sainz, who lost control of his Ferrari in a big way at Turn 3.
It marked the second time in as many weekends that Sainz has suffered extensive damage to his car.
The session had only just got back underway when Hulkenberg then spun coming out of Turn 1, with his Haas car ending up rear-ending the barriers.
Following a much speedier clear-up, the drivers got just 15 minutes of clean running to complete both high and low fuel running.
Leclerc ended up 0.043s clear of McLaren’s Lando Norris, while world champion Max Verstappen was third-quickest in his Red Bull.
Alfa Romeo’s Valtteri Bottas was an eye-catching fourth ahead of the second Red Bull of Sergio Perez and George Russell’s Mercedes.
Zhou Guanyu and Lewis Hamilton were seventh and eighth respectively for Alfa Romeo and Mercedes, while Alpine’s Pierre Gasly and McLaren’s Oscar Piastri completed the top-10.
The interupted session, which took place in conditions representative of those in qualifying and the race, gave little indication of the true competitive order due to teams conducting different run plans.