Sainz topped the podium at last week’s Singapore Grand Prix to end Red Bull’s hopes of an undefeated Formula One season, with runaway championship leader Max Verstappen finishing fifth and Sergio Perez eighth.
The Red Bulls will start as heavy favourites to restore normal order at this week’s Japanese Grand Prix and could clinch the constructors’ championship at Suzuka.
Sainz said beating them in Singapore “gives me a lot of pride” but he did not pin his hopes on a repeat performance with seven races of the season remaining.
“It seemed almost like it was going to be impossible to beat them,” said the Spaniard.
“To go to Singapore and do it in the way we did it is a great feeling, but I wouldn’t be surprised if they win the rest of their races.”
Sainz is currently enjoying a run of form, finishing third at the Italian Grand Prix at the start of the month before winning in Singapore, and claiming pole in both races.
He is fifth in the drivers’ standings, 28 points behind Spanish compatriot Fernando Alonso of Aston Martin.
“It’s always important to keep your head down and try to keep the momentum going, because it’s always difficult to find that momentum in such a competitive environment,” said Sainz.
“Singapore is over. We focus on Suzuka.”
Ferrari are currently third in the constructors’ standings, 24 points behind Mercedes.
Sainz said he and teammate Charles Leclerc have been dealing with a “tricky” car and were “still trying to find the right set-up”.
“The only thing I can say is that we’ve been working hard to try to find the sweet spot,” said Sainz.
“Probably we still haven’t found it yet and that’s why every week I try something different in the car to try to challenge myself, the car and the team.”