Ferrari's Fernando Alonso said he felt McLaren were the early front-runners at what promises to be an incredibly competitive Italian Grand Prix.
McLaren's Lewis Hamilton and Jenson Button set the pace in Friday practice, but Alonso was only 0.058 seconds behind them in third.
Alonso, the world championship leader, said: "McLaren looked very strong so we need to find something extra."
But Button said: "Ferrari's pace is very good. They are very, very quick."
The field is extremely closely matched - just 0.257secs separated pace-setter Hamilton from Force India's Nico Hulkenberg in eighth fastest.
Button said: "There are quite a few cars out there that are quick, it's very, very close. The Mercedes are quick, the Lotus...
"It's going to be an interesting weekend, it's not going to be straightforward for any of us."
Alonso had a difficult day, suffering engine, braking system and gearbox failures, but he said he was hopeful of a good weekend.
"It's good," he said. "More than the performance is just the balance of the car.
"Sometimes we arrive on Friday and we need to change the balance completely for P2 and then completely again for FP3 and then we are in the middle of making decisions in the last moment before qualy.
"So far in FP1 and FP2 we found a car that was consistent and easy to drive, and we see both Ferraris in the top six or seven all the time, which is not always like that. That is the best news in terms of performance."
Alonso is leading the championship by 24 points, slightly less than a win, but saw Red Bull's Sebastian Vettel cut his advantage significantly in Belgium last weekend after the German finished second and Alonso was forced to retire after being hit by Lotus's Romain Grosjean at the start.
But he emphasised that he was still in control of the championship.
"We need to concentrate on our job," he said.
"We did quite a good performance until now in terms of points, a little bit better than our opponents.
"Last weekend we saw how things can quickly change. In two or three races you can lose all the advantage but at the moment we are the only ones who can do that - we can not finish in Belgium and we can not finish here and we are still in title contention.
"If some of the other rivals don't finish a race or two, they say bye-bye, so that is our only advantage."
Hamilton said: "It's been a reasonable day. Lots of people have very good long runs and we just need to continue focusing on our job."