Verstappen set the benchmark pace on medium rubber in the opening stages before improving on his switch to softs, leading Leclerc by 0.347 seconds in a scrappy session for the Ferraris.
At Williamsappendicitis forced Albo onto the sidelines and one-time Formula E champion de Vries into his seat for the rest of the Italian GP.
De Vries, who drove for Aston Martin in FP1 instead of Sebastian Vetteltook to the Monza circuit ahead of his race debut on Sunday with 36 minutes remaining in the hour-long session and immediately went 18th on medium tyres.
A slow start to the final practice of the Monza weekend meant that only six drivers recorded lap times after the first 10 minutes of running.
Red Bull’s Sergio Perez set the early benchmark with 1m23.448s on medium rubber.
He later improved to 1m22.611s and 1m22.148s, with Alfa Romeo. Valtteri Bottas about two seconds drift in a second after initial running on soft rubber.
Pérez’s Red Bull team-mate Verstappen was forced to abort his first flying lap on medium tires just over 10 minutes into the session when he encountered slow-moving traffic in the form of a Mercedes. George Russell.
Bottas was forced to run through the first chicane flat-spotting his soft tires trying to avoid Pérez, with the stewards putting the incident under investigation before opting to recall the Spaniard after FP3.
Sainz’s session was thrown another complication when he was told to pit shortly after with an apparent fuel system problem, although was able to get out on track with about half an hour remaining.
After his opening time attack lap was thwarted by Russell, Verstappen shot to the top of the order with a 1m21.872s on medium tires just under 20 minutes into the session as Leclerc’s Ferrari moved up to second on the same compound.
Verstappen’s position remained intact as Sainz moved up to second on soft rubber with 15 minutes remaining before the Red Bull driver produced a 1m21.252s on his qualifying simulation on the redwall tyre.
This would stand as the best lap of the weekend so far heading into qualifying, with Leclerc holding second to Perez.
Leclerc closed out his first flying lap on soft tires towards the end of FP3, taking the best of the compound for his second attempt.
De Vries improved to 1m22.869s, although he suffered an off-track moment coming out of the first Lesmo with about half an hour of the session still to run.
McLaren’s Daniel Ricciardo led by Bottas, Aston Martin’s Sebastian Vettel, Haas duo Kevin Magnussen and Mick Schumacher – which was kept in its garage until the final 10 minutes due to a clutch problem – and Lance Walk in the second Aston.