Red Bull's Sebastian Vettel says he expects a "tight" battle in Italian Grand Prix qualifying despite a dominant performance in practice.
The German was 0.623 seconds clear of his closest challenger, team-mate Mark Webber, in second practice at Monza.
Vettel said: "I think it will be close [in qualifying, with many cars within a couple of hundredths of a second]."
He said first practice, in which only 0.188secs separated the top four, was potentially more representative.
Vettel was fourth in the first session, behind Mercedes driver Lewis Hamilton, Ferrari's Fernando Alonso and the second Mercedes of Nico Rosberg.
"I felt pretty comfortable but I'm sure it will be very tight," Vettel said. "We saw that in first practice. Second practice if you look at it too much it is a bit of a distraction.
"We'll have to work on ourselves; there are two or three things where we need to find a step.
"Even though the car was great, there were still two or three corners where you slide a bit more than you like. But I would be lying if I said it was a disaster.
"It is a short-ish lap. There are not too many corners, so not that much you can do right, and not that much you can do wrong. If we all get it right, it should be very close."
Hamilton said on his Twitter account: "Car feels good here at Monza. Bit of work to do tonight but we are feeling confident and competitive."
He added in media interviews: "It has been quite a smooth day. We're not as fast as the Red Bulls, but we are still confident.
"The Red Bull is quick but generally the car feels good so I have to sit and try and understand [where to find the pace].
"I feel like I am on the limit everywhere and the car feels reasonably balanced.
But Hamilton said he did not feel particularly optimistic that he could take pole on Saturday, for what would be the fifth consecutive race.
"Right now, it doesn't look massively strong for tomorrow," he said. "But hopefully we can improve the pace."
Alonso was fifth fastest in second practice, 0.877secs slower than Vettel.
The Spaniard has admitted he must try to finish in front of Vettel this weekend to prevent the German extending his lead any further than the current 46 points.
Ferrari team principal Stefano Domenicali admitted Red Bull "seem very strong", adding: "We have two races in front of us [in Italy and then Singapore] where if we are not able to deliver a good result it will be very difficult to stay connected to the leader, so for sure it is very crucial."
The times set on the race-simulation runs, on which teams run race levels of fuel, were more encouraging for Ferrari.
Webber's average over a 16-lap run on medium tyres, on which he appeared to be simulating the first stint of the race was one minute 29.129 seconds, while Alonso's on a similar 14-lap run was 1:29.293.
Hamilton did 1:29.461 and Raikkonen 1:29.544, while Rosberg averaged 1:29.149 on the hard tyre.
Vettel did not do a comparable run - he ran on the hard tyre when Webber and Alonso were on the mediums.
The teams do not reveal the fuel loads they were using at the time, so it is impossible to make an accurate comparison.