The Spaniard arrived at Suzuka in a buoyant mood after leading team-mate Charles Leclerc to a 1-2 finish at the Australian GP, and hopes had been high of a strong showing in qualifying after some promising long-run form in practice.
However, Ferrari endured a more challenging time in the fight for grid positions, as Sainz ended up fourth on the grid, 0.485 seconds adrift of pole position man Max Verstappen. Leclerc qualified eighth.
And while that gap to the front has highlighted just how much more progress Ferrari needs to make before it can consider itself a proper challenger to Red Bull, he thinks that it is a track-specific phenomenon that has been exposed here.
Asked by Motorsport.com if the weekend had been a reality check for where Ferrari really stood against Red Bull, Sainz said: "Yeah. But we will fight for wins in other tracks.
"We will maybe go to the Monzas or the Singapores, and Miami maybe, and we're still in the mix, you know, for [the victory]. But there's other tracks where the Red Bull is just simply a much better package.
"As I said in the press conference [on Thursday], until we develop this car for this kind of track, they will be three-tenths to half a second ahead. So it's time to put our heads down and try to bring a good package to help at this sort of track."
Sainz explained that he never expected Ferrari to shine at Suzuka, with the circuit's high-speed swoops putting a premium on the kind of aero performance that Red Bull's RB20 is so strong at.
"That's why yesterday I was trying to bring everyone down a bit - because I knew that being one second away last year [was not going to be wiped away this year]," he explained.
"I know that we didn't improve one second the car from last year to this year in a place like Suzuka, so it was going to be always tricky.
"But I'm very happy with how the car feels this year. It's a step better. We just need to do another step in this sort of track. Anyway, I did some very clean, good laps today, that put me P4, which is a good position to fight tomorrow."
But as well as Red Bull being clearly in front, Sainz reckoned that Suzuka had shown that McLaren too had an edge at high-speed venues.
"It's clear that in the sort of long high-speed corners, the Red Bull and McLaren are still a step ahead of us," he added. "A clear step ahead of us.
"But hopefully tomorrow we can fight for the podium. I think in the race, Red Bull are still out of reach. But with the McLaren hopefully, we can be a bit closer in the race."
