[[Berkas:FIA F1 Austria 2021 Nr. 55 Sainz.jpg|jmpl|Sainz di [[Grand Prix F1 Austria 2021|Grand Prix Austria 2021]].]]
[[Berkas:Formel12021-SchlossGabelhofen(15).jpg|jmpl|Sainz pada tahun 2021.]]
Sainz bergabung bersama dengan tim [[Scuderia Ferrari]] dengan durasi kontrak dua musim mulai dari musim {{F1|2021}}, menggantikan posisi Sebastian Vettel<ref>{{Cite web|date=14 Mei 2020|title=Carlos Sainz confirmed as Charles Leclerc's Ferrari team mate for 2021, replacing Sebastian Vettel {{!}} Formula 1®|url=https://www.formula1.com/en/latest/article.breaking-sainz-confirmed-as-leclercs-ferrari-team-mate-for-2021.5dSxBMUOyivTKN67Qx28Tl.html|website=www.formula1.com|language=en|access-date=8 April 2022|archive-date=2021-01-16|archive-url=https://web.archive.org/web/20210116155359/https://www.formula1.com/en/latest/article.breaking-sainz-confirmed-as-leclercs-ferrari-team-mate-for-2021.5dSxBMUOyivTKN67Qx28Tl.html|dead-url=no}}</ref> yang pindah ke [[Aston Martin didalam Formula Satu|tim Aston Martin]].<ref>{{Cite web|title=Carlos Sainz confirmed as Charles Leclerc's Ferrari team mate for 2021, replacing Sebastian Vettel|url=https://www.formula1.com/en/latest/article.breaking-sainz-confirmed-as-leclercs-ferrari-team-mate-for-2021.5dSxBMUOyivTKN67Qx28Tl.html|website=formula1.com|access-date=2020-05-14|date=2020-05-14|archive-date=2021-01-16|archive-url=https://web.archive.org/web/20210116155359/https://www.formula1.com/en/latest/article.breaking-sainz-confirmed-as-leclercs-ferrari-team-mate-for-2021.5dSxBMUOyivTKN67Qx28Tl.html|dead-url=no}}</ref> Di [[Grand Prix F1 Bahrain 2021|Grand Prix Bahrain]], ia memulai dan mengakhiri balapan di posisi ke-8. Ia kemudian memulai dari posisi ke-11 di Grand Prix Emilia Romagna dan finis di posisi ke-5, mengejar rekan setimnya, yaitu [[Charles Leclerc]]. Dia mendapatkan podium ketiga sepanjang karirnya, dan yang pertama bersama dengan tim Ferrari, setelah finis di posisi ke-2 di [[Grand Prix F1 Monako 2021|Grand Prix Monako 2021]].<ref>{{Cite web|date=3 Juni 2021|title=Sainz calls Monaco podium ‘good boost’ for Ferrari – but not expecting similar performance in Baku {{!}} Formula 1®|url=https://www.formula1.com/en/latest/article.sainz-says-monaco-podium-good-boost-for-ferrari-but-not-expecting-repeat-in.4HNTvWC3bUWVYLDNcKcBYi.html|website=www.formula1.com|language=en|access-date=27 September 2021|archive-date=2021-09-27|archive-url=https://web.archive.org/web/20210927090345/https://www.formula1.com/en/latest/article.sainz-says-monaco-podium-good-boost-for-ferrari-but-not-expecting-repeat-in.4HNTvWC3bUWVYLDNcKcBYi.html|dead-url=no}}</ref> Banyak yang telah memuji kemampuannya untuk beradaptasi cepat dengan tim Ferrari dibandingkan dengan rekan setimnya, yaitu Leclerc, di balapan-balapan pembuka musim.<ref>{{Cite web|last=Mitchell|first=Scott|date=31 Mei 2021|title=Sainz has shown why he deserves to be taken more seriously|url=https://the-race.com/formula-1/sainz-has-shown-why-he-deserves-to-be-taken-more-seriously/|website=The Race|language=en-GB|access-date=27 September 2021|archive-date=2021-12-19|archive-url=https://web.archive.org/web/20211219224714/https://the-race.com/formula-1/sainz-has-shown-why-he-deserves-to-be-taken-more-seriously/|dead-url=no}}</ref><ref>{{Cite web|last=Gardner|first=Jay|date=26 Maret 2021|title=Carlos Sainz is proving why he’s one of the best drivers on the grid – and it’s time people started noticing|url=https://www.formulanerds.com/features/carlos-sainz-is-proving-why-hes-one-of-the-best-drivers-on-the-grid-and-its-time-people-started-noticing/|website=FormulaNerds.com|language=en-US|access-date=27 September 2021|archive-date=2021-09-27|archive-url=https://web.archive.org/web/20210927090345/https://www.formulanerds.com/features/carlos-sainz-is-proving-why-hes-one-of-the-best-drivers-on-the-grid-and-its-time-people-started-noticing/|dead-url=no}}</ref> Ia finis di posisi ke-4 di [[Grand Prix F1 Hungaria 2021|Grand Prix Hungaria]], namun posisi finisnya berubah menjadi posisi ke-3 setelah Sebastian Vettel terkena penalti.<ref>{{Cite web|last=Matt|first=Morlidge|date=2 Agustus 2021|title=Hungarian GP: Sebastian Vettel disqualified after insufficient fuel sample after race, loses P2|url=https://www.skysports.com/f1/news/12433/12370358/hungarian-gp-sebastian-vettel-disqualified-after-insufficient-fuel-sample-after-race-loses-p2|website=Sky Sports|language=en|access-date=27 September 2021|archive-date=2021-09-27|archive-url=https://web.archive.org/web/20210927090353/https://www.skysports.com/f1/news/12433/12370358/hungarian-gp-sebastian-vettel-disqualified-after-insufficient-fuel-sample-after-race-loses-p2|dead-url=no}}</ref> Sainz memulai Grand Prix Rusia di posisi ke-2, dan berhasil menyalip Lando Norris di putaran pertama. Namun, pada akhirnya, Sainz menyelesaikan balapan di posisi ke-3, podium ketiganya bersama dengan tim Ferrari.<ref>{{Cite web|date=2021-09-26|title=Sainz thought podium chance was lost after early pit stop in F1’s Russian GP|url=https://www.crash.net/f1/news/988483/1/sainz-thought-podium-chance-was-lost-after-early-pit-stop-f1-s-russian-gp|website=Crash|language=en|access-date=2021-09-27|archive-date=2021-09-26|archive-url=https://web.archive.org/web/20210926212011/https://www.crash.net/f1/news/988483/1/sainz-thought-podium-chance-was-lost-after-early-pit-stop-f1-s-russian-gp|dead-url=no}}</ref><ref>{{Cite web|last=Fadli Ramadan|first=Muhammad|date=27 September 2021|title=Carlos Sainz Sebut GP Rusia Jadi Balapan Terbaik bersama Ferrari|url=https://id.motorsport.com/f1/news/carlos-sainz-nilai-gp-rusia-balapan-terbaik/6676840/|website=id.motorsport.com|language=id|access-date=27 September 2021|archive-date=27 September 2021|archive-url=https://web.archive.org/web/20210927090353/https://id.motorsport.com/f1/news/carlos-sainz-nilai-gp-rusia-balapan-terbaik/6676840/|dead-url=no}}</ref>
