Sainz qualified second for his home race, but as has been the case in previous races, Ferrari's comparatively poor race pace made him slide backwards, his Ferrari struggling with the bumpy and fast nature of the Barcelona circuit as it was outclassed by Mercedes on tyre management.
After an early first pitstop, Sainz went from the soft onto the hard tyres, which allowed Mercedes' Lewis Hamilton to breeze past him on fresher and faster mediums later on.
Team-mate George Russell also followed Hamilton through to claim a double Mercedes podium behind runaway leader Max Verstappen, and Sainz was demoted to fifth in the closing stages by the second Red Bull of Sergio Perez, who had started as far back as 11th.
While Sainz was slowly losing ground, team-mate Charles Leclerc struggled to make inroads from his pitlane start, finishing just outside the points in 11th.
Sainz said the race exposed Ferrari's propensity of chewing through its tyres, a recurring issue which was exacerbated by Barcelona's many high-speed right-handers, which were tough on the left-front corner.
"Honestly, I just spent the whole race managing tyres because we know we are very hard on them and with this high deg circuit, I just couldn't push," Sainz said.
"We know it's a weakness of our car and coming to a high deg circuit and a two-stop race, we were just managing the whole way trying to make it to the target laps of the stints and still falling short in a few of them.
Source: Autosport