Max Verstappen has ended opening practice for the Italian Grand Prix at Monza fastest ahead of Ferrari's Carlos Sainz.
The Dutchman was only marginally quicker than his scarlet-clad rival with just 0.046s splitting the pair.
It was a busy session though one that proved difficult to extrapolate from given the alternate tyre allocation in use this weekend.
As such, there was a different approach to the start of the weekend, with McLaren bolting on softs for Oscar Piastri while Red Bull and Ferrari opted for hard tyres.
The two Red Bulls set the early running, Verstappen mustering a 1:23.027s to head team-mate Sergio Perez by almost 0.2s after 10 minutes.
With a significant low downforce package this weekend, Lando Norris headed out with an aerodynamic rake on his car as the team evaluated its revisions.
He was among the first on track, leading Felipe Drugovich for Aston Martin in his first F1 race weekend outing of 2023.
The Brazilian won last year's Formula 2 championship and climbed into the AMR23 usually occupied Lance Stroll.
Williams was in no rush to head out, both Alex Albon and Logan Sargeant remaining in the garage to preserve their tyres.
Both drivers emerged with 40 minutes remaining with soft compound tyres.
As he did so, the order remained Verstappen at the top of the totem, on a 1:22.657s, with Perez second at 0.297s back.
Charles Leclerc was next, also on the hard tyres, the Ferrari driver having logged 10 early laps.
The Finn suggested something was stalling at the back of the car, which sports a revised livery to celebrate the launch of an Alfa Romeo road car.
He subsequently termed the car “undriveable”, a word used by Zhou who was suffering heavy bottoming.
With 20 minutes to run, Carlos Sainz split the Red Bulls to move to within 0.05s of Verstappen's best.
Running was, to a degree, compromised by the tyre allocation with teams sacrificing what they considered the least desirable rubber, and for the most part only a single set.
Peak pace was therefore not representative, nor was it easy to draw comparisons between those on different compounds.
Those at the top of the timesheets were on the hard rubber, Fernando Alonso sixth best with 10 minutes remaining the first to differ from that. One spot back was Norris, who'd used the soft tyres.
Focus was therefore on longer runs, saving their rubber for qualifying on Saturday, and simulations in later sessions when the track had evolved more.