On 13 August 2017, Immobile scored the opening two goals of the Supercoppa Italiana; Lazio won with a final score of 3–2 over Juventus. On 10 September, in Lazio's third match of the season, he scored a hat-trick and got an assist in a 4–1 home win over Milan. On 21 October, Immobile extended with Lazio until 2022. On 6 January 2018, Immobile scored four goals in the first half away to SPAL, the first Lazio player to score multiple hat-tricks in a season in 16 years; Lazio eventually won the match 5–2. On 22 February 2018, Immobile scored a hat-trick in the Europa League round of 32 second leg home to Steaua București in a 5–1 win, which allowed Lazio to qualify, 5–2 on aggregate, to the round of 16. On 31 March 2018, Immobile scored twice in Lazio's 6–2 home win over Benevento, his 36th goal of the season, breaking Giorgio Chinaglia's previous record for most goals scored by a Lazio player in a single season, by two goals. Immobile ended the season with 29 goals in 33 appearances, winning the "Capocannoniere" jointly with Inter's Mauro Icardi.