Sainz went quickest in Friday afternoon's one-hour FP2 session, his 1m21.355s just 0.019s quicker than McLaren's Lando Norris.
The first Red Bull of Sergio Perez was 0.185s behind in third, followed by the second McLaren of Oscar Piastri and Perez' team-mate Max Verstappen.
But when asked if Ferrari's tifosi can start dreaming after the Scuderia's impressive practice performance, Sainz pointed out Red Bull's long-run pace is still far superior.
"Dreaming is for free, no? This is one of my favourite sayings. I think we can all dream and it's for free, no one can it take away from us.
"But being realistic, also looking at our race pace, that's when we start to see the true pace of the Red Bull again.
"They were clearly again three-tenths of a second ahead in race pace and over 50 laps that's a lot of lap time."
Sainz's comments correlate with data that Autosport has had access to, which corrects the long-run averages for fuel loads and engine modes and also puts Red Bull several tenths quicker on average in the FP2 long runs.
Nevertheless, Ferrari's strong Friday performance is encouraging after a torrid Zandvoort weekend, with its notorious form fluctuations between race tracks a key area to address for 2024.
"It was great to be back on a track like Monza and to feel from the first lap of FP1 that our car is normal again after such a difficult weekend," Sainz conceded.
"As soon as we put the car on track here for some reason it just adapted a lot better, and it was a lot easier to set up and drive it through a corner.
"It's the same car basically but for some reason, it just felt a lot better which is what puzzles us.
"But let's see tomorrow, everyone's going to be low fuel, higher engine modes. It's going to be a bit of a different picture but at least the feeling is decent."
Team-mate Charles Leclerc finished Friday sixth-fastest, 0.361s behind the Spaniard.
He admitted he still had pace to find on low-fuel runs, having focused more on race pace on a weekend where the number of available tyre sets has been reduced due to Pirelli's alternative tyre allocation.
"It was really good on high fuel, on my side I struggled quite a bit more on low fuel," Leclerc explained.
"I think we know what to do. We went a bit in a different direction, so we need to reset a little bit for tomorrow and focus especially on the low-fuel runs.
"We need to adapt a little bit more because we're running less new tyres, so a bit less preparation for qualifying.
"We will also be running the hard tyres in Q1 which we only ran once, and the medium tyres in Q2 that we also only ran once, so it's going to be interesting."
