Mercedes' Valtteri Bottas set the pace in a competitive but disjointed final practice session for the Italian GP, with McLaren taking impressive second and third-fastest times as the Renault-powered cars ran strongly.
Lewis Hamilton was only fifth and Max Verstappen sixth with the championship-leading duo pushed down by McLaren's Carlos Sainz and Lando Norris, along with Renault's Daniel Ricciardo, in the closing minutes of the session.
But Ricciardo was forced to park up on the grass inside the final five minutes with a fuel-pump failure. Fortunately, Renault expect the part to be replaced in time for the Australian to take part in qualifying.
Hamilton also found himself on the grass - but this was because he had to take high-speed evasive action to avoid cars slowing before the Parabolica amid the increasingly fraught and controversial battle for the 'tow' around high-speed Monza.
The queuing in qualifying is set to be a big factor for the second successive year. Qualifying begins at 2pm live on Sky Sports F1, with build-up from 1pm.
"It's totally out of order, and there might even be a penalty for that," said Sky F1's Jenson Button of Romain Grosjean moving to the right ahead of the fast-oncoming Hamilton.
Bottas' session-topping lap was 1:20.089 but Mercedes, absolutely dominant on Friday, appeared to be holding back on performance relative to the chasing pack in the final practice session.
Sainz and Norris finished within four tenths of the pacesetter, with Ricciardo close behind before his stoppage.
Hamilton's first attempt at a soft-tyre lap was compromised by a poor exit from the first chicane, while Verstappen didn't set a fast time on the quickest compound. But the Dutchman's pace on the medium tyre beforehand was impressive - he had led the way on the timesheet. before the qualifying simulations.
Alexander Albon was seventh, although lost time through a mistake at Parabolica, with Esteban Ocon eighth in the second Renault.
Both Ferraris were outside the top 10, although Charles Leclerc was at least within striking distance of the Racing Points in 11th. Sebastian Vettel, however, struggled again and was 15th between the similarly Ferrari-powered Haas cars and looks an unlikely contender for Q3.