Pirelli, Formula One’s sole tyre supplier, had initially suggested an increase in 5 psi after they suffered two high-profile blow-outs at the last meeting in Belgium.
Hamilton on Thursday warned that such a decision could have disastrous consequences. Following discussions with the teams in Monza yesterday, Pirelli opted to recommend a smaller increase.
Hamilton, who was fastest in both sessions at Monza, said: “The team worked hard to speak with Pirelli and get them to bring the pressures down.
“There was much more sensible change when they came down with it this morning. It is only 1 psi more so they have come down quite a bit.
“So, it is not a huge difference, but it would have been if it was 5 psi like they suggested.”
Hamilton, 28 points ahead of Nico Rosberg in the race for the championship, finished the opening session almost 0.5 seconds clear of his Mercedes team-mate.
Rosberg will draw confidence from the fact he was only 0.021secs shy of Hamilton’s best lap of 1:24.279 yesterday afternoon.
Mercedes have brought an upgraded engine with them to Italy, and Hamilton and Rosberg were in a league of their own in Monza.
Sebastian Vettel, competing in his first race for Ferrari in front of the partisan Tifosi, was three-quarters of a second slower than the Mercedes duo.
Rosberg said: “We are surprised by the gap as we are looking very quick at the moment.
Force India, powered by Mercedes engines, appeared strong in opening practice and followed that up in the afternoon with Sergio Perez fourth and Nico Hulkenberg, who penned a new two-year contract with the team this week, in fifth.
McLaren’s already difficult day took a turn for the worst during the second session when Jenson Button’s running was restricted to just three laps.
The 2009 world champion, who will serve a five-place grid penalty for Sunday’s race, was called into the garage and failed to re-emerge. He finished over four seconds adrift of Hamilton in 19th and his team-mate Fernando Alonso fared little better.
The Spaniard, slapped with a 10-place grid drop after taking on his ninth engine of the campaign, was only 16th, 2.6secs slower than Hamilton.
McLaren will be joined at the back of the field for Sunday’s race by Red Bull. Daniel Ricciardo has been penalised 25 places following an engine change and raft of new components. Team-mate Daniil Kvyat, who propped up the timings in the second session, faces a 15-place grid drop.