Red Bull's Sebastian Vettel was in daunting form as he headed team-mate Mark Webber in second practice at the Italian Grand Prix.
The world champion was 0.623secs clear of Webber, with Lotus drivers Kimi Raikkonen and Romain Grosjean just behind on identical times.
Vettel's main title rival, Ferrari's Fernando Alonso, was fifth quickest, 0.877secs slower than the German.
Mercedes' Lewis Hamilton was sixth and McLaren's Jenson Button eighth.
Red Bull had not expected this race to be one of their strongest, but their performance in practice was as impressive as any they have produced this year.
Vettel - who was fourth fastest in the first session behind Hamilton, Alonso and the second Mercedes of Nico Rosberg - was comfortably quickest on both the 'hard' and softer 'medium' tyres.
Raikkonen had said on Thursday he thought Lotus would struggle, but in second practice they were the world champions' closest challengers, 0.663secs slower than Vettel.
The Finn was running a car with a longer wheelbase, aimed at producing better downforce and improved braking stability, while Grosjean was in the standard car - but they set identical lap times to the thousandth of a second.
Alonso has admitted he must beat Vettel this weekend and reduce his 46-point deficit in the championship, but on the basis of lap times on Friday that will be a tough ask.
BBC 5 live analyst and former F1 driver Allan McNish said: "Right now I have to say I don't think Ferrari have the absolute pace of the Red Bull.
"I think it will be a lot closer in qualifying than the 0.6secs gap we see between Vettel and the rest on Friday but it really needs to be if people are going to try to challenge him in the race."
Hamilton comes to Monza on the back of four consecutive pole positions, but he seemed to struggle for pace in the second session - nearly 0.9secs off Vettel and 0.027secs ahead of Rosberg, who split him from Button.
BBC F1 analyst Gary Anderson said: "It's Friday, so we have to take the times with a small pinch of salt, but whoever is quick, is quick, and it looks like Red Bull are in a fairly dominant position, which is not great for everyone else.
"I still think there is something in the Ferrari, though. And I expect the lap times to be closer in qualifying than they are today.
"Interestingly, the Red Bulls are running with a greater disparity of aerodynamic set-up than I have seen for some time. Vettel appears to have less front wing and more rear wing and Webber the other way around. It will be interesting to see if they converge on Saturday - as in fact they did in Spa last time out."
Ferrari have been fined 10,000 euros for an incident where Felipe Massa nearly hit team-mate Fernando Alonso at the exit of the pit lane after the session had officially ended.