Mercedes dominated Friday practice at the Italian Grand Prix, with Valtteri Bottas topping the second session and Lewis Hamilton quickest in the first.
Bottas beat the Briton by 0.056 seconds in the afternoon, when Hamilton's title rival Sebastian Vettel of Ferrari was just 0.14secs off the pace.
Hamilton led Bottas by 0.435secs in the morning, with Vettel a second slower.
Ferrari's Kimi Raikkonen was fourth, ahead of Red Bull drivers Max Verstappen and Daniel Ricciardo.
Dutchman Verstappen and Australian Ricciardo face starting from the back of the grid because of a series of penalties for using too many engine parts.
McLaren's Fernando Alonso will join them for the same reason.
Hamilton has identified this race as a must-win, aiming to go into the Asian long-haul races with an advantage in the expectation that Ferrari will be difficult to beat in the next grand prix in Singapore.
"It's been a good day, a clean day," said Hamilton.
"We got the running done, we got through our programme with no problems. The car seems nicely balanced here. We just have some work to do to eke out a little bit more performance.
"It looks quite close between us and the Ferraris, so I anticipate it's going to be similar to the last race in that sense."
Hamilton looked like he could have beaten Bottas' headline time in the second session had he put together a clean lap on his qualifying-simulation run; as it was he made a couple of mistakes.
"Valtteri had lots of tows during the lap and I just didn't have a good lap," he added.
"P1 was really good. P2 was a little tricker with the track being hotter, so the balance of the car was a bit inconsistent. So it is harder to guess where we have the car for Saturday and Sunday so my mind is moving pretty fast."
Mercedes appear to have the edge over Ferrari on both qualifying and race pace so far on the historic Monza track, famous for its enthusiastic Ferrari fans, the tifosi.
On first indications, Hamilton and Bottas appeared to be a few tenths of a second quicker than Vettel on both the soft and super-soft tyres when they ran with race fuel loads later in the session.
"Our day has been a bit mixed," said four-time champion Vettel. "We need to improve a little bit here and there, then we should have a better day tomorrow.
"We are OK. There are a couple of things we need to of better - car balance, stability and braking which is important around here to get the confidence because you are on low downforce and you need to have the confidence to throw the car in without thinking.
"We are not quite where I think we can be."
The McLarens showed a surprising turn of pace on a track that exposes the lack of power from the Honda engine - Alonso was eighth fastest and team-mate Stoffel Vandoorne seventh, 0.021secs ahead.
The two spent some of their time practising slipstreaming techniques, which they will use to try to get the Belgian as high up the grid as possible on Saturday.
Williams, after a terrible race in Belgium last weekend, looked more competitive, with Felipe Massa ninth fastest behind the Force India of Esteban Ocon.
Massa's team-mate Lance Stroll was 0.5secs slower, and down in 15th, after a high-speed spin at the Ascari chicane.