Alonso was signed to drive for Alpine F1 Team for the season, alongside Esteban Ocon, with Renault having rebranded the team under its new name. In preparation for his Formula One return, Alonso performed four testing days driving the Renault R.S.18 and topped the timing charts in the post 2020 season young driver's test driving the Renault R.S.20 for Renault. In his first race with Alpine, Alonso was forced to retire after plastic debris entered his brake duct. At the 2021 Emilia Romagna Grand Prix he finished in P11 after qualifying P15, with teammate Ocon finishing ahead in P10, but both were upgraded one position after Kimi Räikkönen was penalised, giving Alonso his first points of the season. At the 2021 Hungarian Grand Prix, Alonso temporarily led the race before pitting and dropping to fourth, ahead of Lewis Hamilton. Teammate Ocon credited Alonso's defence against Hamilton with enabling him to achieve his first race victory. In August 2021, Alonso invoked an option to extend his contract for the season.