Verstappen closed out the opening 20 minutes of the hour-long FP1 session with a 1m22.657s, bettering his previous effort of 1m23.027s on the hard compound of tyres.
His Red Bull team-mate Sergio Perez had got to within three tenths to slot into the runner-up spot in the session, but was beaten by Sainz’s 1m22.703s just after the opening half-hour had elapsed.
The alternative tyre allocation for the Monza weekend, following on from the first trial in Hungary, restricted drivers to the number of tyres they could burn through during the session as the customary 13 sets per car were reduced to 11.
This prompted a variety of approaches from each team, as some elected to save tyres in the opening part of the session to potentially keep an extra set free in qualifying.
Verstappen and Perez elected to stick with a set of hard tyres for the opening part of the session, and traded times at the top with the Ferraris, Mercedes and Oscar Piastri on softs.
Sainz was first into the 1m23s on his hard compound of tyre, but Verstappen then found half a second on the Ferrari driver. During that opening 15 minutes, Piastri grabbed a 1m23.446s but this was again beaten by Sainz as the Spaniard got into an early groove in front of his team’s home crowd.
Verstappen then pitched up with a 1m23.027s, and then chipped almost 0.4s off his time during his next flying lap to extend his advantage over team-mate Perez. The two were then split by Charles Leclerc, the next driver to dip below the 1m23s barrier. Perez improved to reclaim second in the session, but was then eclipsed by Sainz’s time.
Leclerc required a lay-off in the garage for adjustments to his car but nonetheless remained 0.309s off the pace as the two re-liveried Ferraris – augmented with a splash of yellow in tribute to the Scuderia’s Le Mans 24 Hours win this year – completed the top four.
George Russell was fifth fastest and ensured the top five times were all set on the hardest C3 compound, over the medium-shod Fernando Alonso. Lando Norris claimed the seventh-best time on softs, over countryman Lewis Hamilton.
Yuki Tsunoda set the fastest first-sector time of the session and used two sets of soft tyres en route to the ninth-fastest time of the session, as Alex Albon completed the top 10.
The Williams duo of Albon and Logan Sargeant held off from joining the fray in the opening 20 minutes, but eventually surfaced on the soft compound. The pair were split on the timing boards by Piastri, who focused on longer runs following his brief stint on top of the times.
Liam Lawson, who continues to stand in for Daniel Ricciardo at AlphaTauri, was 13th fastest over Pierre Gasly, who put 24 laps on a single set of soft tyres over the session.
Valtteri Bottas claimed 15th following early issues at Alfa Romeo; both cars were afflicted by clutch software issues, which kept throwing up anti-stall modes as Zhou Guanyu and Bottas both tried to exit the pits.
While the issues were fixed, both drivers had grievances with the rear-end balance of the car and cited that the C43 was “undriveable” in unison, Bottas complaining of aerodynamic stalling and Zhou of the car bottoming out. Following adjustments to the car, both drivers reported that the car felt stronger.
Nico Hulkenberg and Esteban Ocon were 16th and 17th, while Aston Martin reserve Felipe Drugovich was 18th fastest as he stood in for Lance Stroll for the opening part of practice. Kevin Magnussen and Zhou completed the order.
