Sebastian Vettel kept Ferrari on top heading into qualifying after setting the fastest time in final practice at the Italian Grand Prix.
More overnight rain had washed the circuit but, for a damp patch on the approach to Turn 1, conditions were dry at Monza allowing the teams to conduct for important running on the slicks.
It would cause a few problems, however, with Stoffel Vandoorne wearing a front-left tyre down to the canvas with just a single lock-up into the first chicane as the two McLaren's and Nico Hulkenberg set the early pace.
Soon though, the top teams came out to play and Kimi Raikkonen lowered the best time by over two seconds with his first flying lap in the mid 1m21's.
Hamilton was unable to match the Finn with his initial effort in second as Vettel struggled for pace, having locked up into the first chicane on his opening flying lap.
Max Verstappen suggested Red Bull may have some strong pace, sitting third on the Soft tyre, however, that gap would soon grow significantly larger as the second set of Supersoft tyres were fitted.
Vettel found his groove and went fastest ahead by three-tenths of Hamilton, who had squeaked ahead of Raikkonen by 0.007s, as lap times dropped into the 1m20's for the first time this weekend.
The 2007 world champion then made it a Ferrari 1-2 with less than a tenth between the two Prancing Horses.
As the grip level improved, the Spa race winner then set the session's best time of 1m20.509s with Hamilton moving up to second just 0.081s back and crucially splitting the two red cars.
Raikkonen a was tenth back in third but comfortably ahead of Valtteri Bottas as his fellow countryman struggled for pace, ending the session six-tenths off the pace in fourth.
Verstappen sat fifth, a position he is almost certainly going to take in qualifying as teammate Daniel Ricciardo will limit his running to just Q1 as he prepares to start from the back.
Another battle between Haas and Force India is emerging for 'best of the rest' with Kevin Magnussen taking that distinction in sixth, less than half a tenth clear of Esteban Ocon for the pink panthers.
Ricciardo sat eighth with Charles Leclerc hinting another Q3 appearance is possible in ninth and Romain Grosjean, despite a brief altercation with Brendon Hartley, completing the top 10.
Sergio Perez sat 11th ahead of Pierre Gasly as the Honda-powered Toro Rosso appears a match for the Renault works team with birthday boy Carlos Sainz in 13th.
Williams are showing better pace too with Sergey Sirtokin and Lance Stroll making it up into what would be Q2 places in 14th and 15th respectively.
For Marcus Ericsson, the morning was about making up for lost time after his big crash on Friday as he sat 16th in front of both McLaren's as Alonso led Vandoorne.
Nico Hulkenberg suffered a DRS failure which left him stuck in the garage in 19th as Hartley completed the order in the second Toro Rosso.
The full results can be seen below:
