Sebastian Vettel says he was "surprised" by Lewis Hamilton's pace and struggled to identify Ferrari's problems after their disappointing qualifying at the Italian GP.
The championship leader qualified down in eighth, behind team-mate Kimi Raikkonen, and will start Sunday's race in sixth as both Scuderia drivers floundered in the wet conditions at Monza.
After the Red Bull penalties, four drivers separate Vettel from pole-sitter and title rival Lewis Hamilton as both Lance Stroll and Esteban Ocon out-qualified the Ferraris.
What's more, Vettel was more than two seconds adrift of Hamilton in Q3 and the Mercedes driver can take the lead in the drivers' standings if he wins Sunday's race and the German finishes second or lower.
Hamilton sets new F1 pole record at Monza
"I don't know what the problem was," Vettel told Sky F1's Natalie Pinkham. "I was surprised by how quick the others went. Clearly we couldn't go the same pace, at this stage we don't know why.
"I'm sure there are a couple of things we will look into and try understand. Nevertheless, I think it was an important day.
"Obviously something didn't work and didn't come together but it it is what it is and we'll see what we can do tomorrow."
Raikkonen was similarly mystified with Ferrari's pace, with both drivers nowhere near their rivals on the wet and intermediate tyres in a qualifying session that was delayed by more than two hours.
"We're not fast enough," the Finn added. "For my car, I struggled a lot with the grip. Maybe we don't make the tyres work - whatever it is it's very slippery."
'Ferrari don't need to be afraid'
Perhaps one saving grace for Ferrari, who would have at least expected a second-row start behind Mercedes at their home grand prix, is that Sunday's forceast looks to be dry.
Vettel's race simulation pace in Practice Two was similar to, if not quicker, than Hamilton's, and he will hope to pass a Williams and a Force India at the very least in the race.
"We have a good car so I don't think we need to be afraid," Vettel added. "Today obviously didn't go the way we wanted but for tomorrow I think we can make up a lot of ground.
"The car is quick, we know that. You can overtake here so it should be a fun race."
Italian GP provisional starting grid - top 10
1) Lewis Hamilton, Mercedes
2) Lance Stroll, Williams
3) Esteban Ocon, Force India
4) Valtteri Bottas, Mercedes
5) Kimi Raikkonen, Ferrari
6) Sebastian Vettel, Ferrari
7) Felipe Massa, Williams
8) Stoffel Vandoorne, McLaren
9) Sergio Perez, Force India
10) Daniil Kvyat, Toro Rosso