Croatia's sensational skipper Luka Modric failed to make a difference as the 2018 Russia World Cup runners-up were held to a scoreless deadlock by tenacious Morocco.
Chances were sparse with Real Madrid's Modric among those coming closest in the opening match in Group F, which also features Belgium and Canada who meet later in the day.
The Atlas Lions contained Croatia well for most of the game but also failed to manage a breakthrough in Al Khor.
A long-distance attempt from Ivan Perisic went over the crossbar before Croatia came closest just before intermission, Nikola Vlasic was denied by goalkeeper Yassine Bounou from close range after a fast move, and Modric then blazing high from the edge of the area.
The 37-year-old Modric and his team also lacked ideas in the second half and their goalkeeper Dominik Livakovic had to palm away a fierce but not very accurate free kick from Paris Saint-Germain defender Achraf Hakimi in the 65th.
Chelsea winger Hakim Ziyech, back in the Morocco squad under new coach Walid Regragui, also failed to make a decisive impact as the game ended in the third 0-0 of the tournament.
