Ferrari had come in to the Singapore weekend braced for a tough time, with its SF-23 having appeared to struggle against the opposition at high-downforce tracks.
However, Sainz and team-mate Charles Leclerc were the surprises of the opening day of action as they headed both practice sessions around the Marina Bay circuit.
But while encouraged about the potential shown, and others suggesting the squad is now favourite for the race win, Sainz and Leclerc are still cautious because they know how much the form book can change over the weekend.
In particular, Sainz says that the way that falling track temperatures and a more rubbered-in track surface can make such a difference to the pace of cars through qualifying shows that Ferrari can take nothing for granted despite its early strength.
Read more: What we learned from Friday F1 practice at the 2023 Singapore Grand Prix
Asked after practice if he was surprised by Ferrari’s pace, Sainz said: “Yeah, a little. But at the same time, I think you always need to arrive to Singapore very open-minded.
“We've seen in the past very weird performance during Saturday's track [action], because it's a very particular track.
“But so far, it looks like it's suiting our car well, and it's going well with the way that we hit the ground running in FP1 and we could just fine tune the set-up a bit for FP2 and be a bit quicker.
“It looks good, but I do believe the track is going to change a lot. It's going to ramp up the grip a lot. And it's all about who finds the perfect set-up.”
Sainz thinks that Friday’s formbook was also slightly skewed by the fact that a number of Ferrari’s rivals were running upgrades, so probably devoted more effort to evaluating those than chasing performance.
“It definitely looks like there's people out here that have a lot of upgrades,” he said. “So, we might see that [for Saturday] they fine tune them, they understand them better and they find a lot of performance.
“For us, we haven't really brought anything, it's just a small tweak to what we had. We are focusing on understanding our car around here. We tested a couple of things of set-up that I wanted to try around this kind of track, and it looks like it worked and it's going in the right direction. So, let's see if we can put another good lap and be on the front row.”
Leclerc echoed that a change of set-up approach for Singapore had appeared to unlock the potential that he had felt was missing at the Italian GP, where he was edged out by Sainz throughout the weekend.
“It changed quite a bit from Monza where I struggled,” he said. “I had a very difficult car on Friday, but we learned from it and we went the other way for here.
“The balance felt great straight away. So, I’m very happy with the change of approach, and it's good to build a weekend starting on a Friday like this.
“But again, we still need to do a step forward. So that's where we are focusing everything at the moment. And let's see what we can do.”
