Ferrari brought a new engine to their home race and went one-two in the morning. Mercedes took the lead back in the afternoon. Two sessions, and 0.141s covering the top three by the end of it.
In FP1, Leclerc had 1:23.008, Hamilton +0.173, Russell +0.304, Lawson fourth, and Antonelli fifth. An important detail here was that Leclerc set it on mediums, and Ferrari never ran the soft compound at all while nine other drivers did. Russell's third was on softs, the faster tire, and was still three tenths adrift. Leclerc did 26 laps, more than anyone. Norris was quickest when the red flag came out, then dropped to sixth as the track improved and Ferrari found time.
The reason Ferrari was so quick in FP1 was their engine upgrade. It's the second of two upgrade opportunities the FIA granted them after judging them more than 4% behind Red Bull. They also brought Monza-specific chassis parts.
In FP2, Russell got the fastest time with 1:22.559, 0.120 clear of Leclerc. Antonelli was third at +0.141, with Norris fourth, Hamilton fifth, and Piastri sixth. Everyone was on softs, and 0.896s covered the entire top ten.
There were four rookies who had to do a mandatory run on track: Iwasa in Verstappen's Red Bull (17th), Herta in Perez's Cadillac, Browning in Albon's Williams (15th), and Aron in Gasly's Alpine (10th), who was the quickest of the four. Herta stopped after about twenty minutes with a hydraulic problem. The car was stuck in gear and hard to move, turning a VSC into a red flag. He'd already crashed heavily in F2 practice that morning.
Ferrari fastest in the morning, Mercedes in the afternoon, and barely a tenth between them. At a track where nobody can pass, Saturday matters more than usual. And the third-quickest car on Friday starts last on Sunday.