Sainz started the race third on the grid with Intermediate tyres, but he simply was unable to keep up with teammate Charles Leclerc and Red Bull's Sergio Perez, who pulled away and ended over 10 seconds ahead of the Spaniard at race end.
The Ferrari driver was kept busy fending off the attacks of Mercedes' driver Lewis Hamilton until the Briton hit the barriers at Turn 7 of lap 33 to fall away and give Sainz less to worry about.
After the Safety Car restart, Sainz was briefly challenged by the McLaren of Lando Norris but he also fell away for the Ferrari driver to go on and claim third place and the podium.
Sainz admitted to having had a lonely race due to his lack of pace.
"It was unfortunately quite lonely for me because I just didn't have the pace," he told the F1 website.
"Today [Sunday] on the intermediate tyre, I lost a lot on the road to Charles and Checo. I couldn't keep up with them. I was struggling quite a lot on these tyres.
"I think I lost quite a bit the front and I was having a lot of moments, a lot of front locks, and every moment here costs you confidence and costs you the ability to recover that pace," Sainz explained.
"At one point I had to settle a bit and recover that confidence because I couldn't keep up and once the confidence recovered in the slick and towards the last 10-15 laps, I managed to be quick, but it was just way too late."
Sainz added that he did not feel physically challenged on the Marina Bay Street Circuit despite the extreme humidity and high temperatures.
"I don't feel like the track is physical at all," Sainz added. "It's usually warm in the car but this is not a problem because the physicality of it is much lower [in wet conditions]; it was just a matter of pure, pure pace and confidence.
"I think here confidence is key, and when you have a couple of moments, it snowballs and then you have to take a bit more margin and then you start losing extra pace compared to other tracks because next time around, you might be in the wall and you might look like an idiot.
"So, it's a confidence thing that I will work on, I will have a good look with my engineers to see what I could have done better, what we can do in these sort of conditions, because [mixed conditions] is one of my strongest points as a driver.
"And I think it's going to be only a one off."