The Spaniard was outperformed all weekend by Ferrari team-mate Charles Leclerc, who took pole for both the sprint and the Grand Prix, and finished second in the shorter race and third in the main event.
Sainz in contrast had to settle for fifth place in both after experiencing a difficult weekend that was exacerbated by the lack of practice running and the imposition of parc ferme after FP1 preventing set-up changes.
In the Grand Prix he lost out to countryman Fernando Alonso, who muscled past after the resumption following the safety car period.
"Seeing where Fernando finished, I think he was always going to finish ahead of me today,” said Sainz when asked about his race by Autosport.
“But yeah, nothing new. Really, the first stint on the medium, I looked like I found a bit of pace back.
"And then as soon as I put the hard on, my struggles of the weekend appeared again, and I just had to bring home a P5, always very on the limit of crashing, or feeling like I was losing the car.
“So [it was] a pretty long race and mentally stressful after the struggle of the weekend. But I brought home the P5. I'm sure we will find out why this happened this weekend. And I'm sure in Miami, we'll be back on form."
While Leclerc had two solid races, Sainz stressed that Ferrari still has to improve its pace over long runs.
"I think we still have a lot of work to do in the race,” he said. “When you see how much quicker we were compared to the Astons in quali, and the Astons being on the tail of Charles all the race, just proves that the car still has a fundamental weakness in race pace.
“So I expect us to make sure that we keep making small steps in the right direction. At least our qualifying pace looks like we've unlocked a bit. But points are on Sunday, and we will work hard on that."
Sainz noted that in Sunday's Grand Prix he had particular issues at Baku’s Turn 15, where several drivers brushed the barriers during the race.
"It's a very tricky corner, it became a really narrow one today,” he said. “There was a bit of tailwind there pushing us from behind. And it meant that it was very easy to clip the wall on the outside.
“And that's why when you're struggling for confidence like I was today, you just need to back off because in any moment you can put it in the wall and throw to the bin 10 points.
“I think last year I would have made a mistake because I was less experienced in a weekend like today, and this weekend I took it easier and made sure that I didn't do the mistakes I did last year."
Asked if he had any clues as to why he struggled in Baku, Sainz hinted that the sprint format hadn’t helped.
"No, because we haven't had time to sit down and analyse,” he said. “We've had to very quickly go into the next session to fine tune the car with the front wing, and the switches, to put it in a bit of a better place.
“But we haven't dug deep into the data to see what could have happened this weekend. But yeah, I'm sure together with my engineers we will find out.
"And we will work be back on form in Miami. It's obviously a shame to have such a frustrating long weekend here in Baku.
"In a way, I find it positive that the next race is coming quickly because I can get this one behind me very quickly."
He added: "I think I need a bit of a normal weekend to get back with a feeling with the car, and if the feeling is the same as here, then I will have a few sessions to experiment with setup."
