 In the first two Masters 1000 events of the season Čilić was defeated by Philipp Kohlschreiber (at Indian Wells, in the round of 32) and John Isner, the eventual champion of Miami.In the clay-court season, Čilić played four tournaments reaching the quarterfinals of Monte Carlo, the semifinals of Rome, and the quarterfinals at the French Open.Čilić failed to defend his only title from the 2017 season at Istanbul, losing in his opening match to Malek Jaziri.