Croatia, runners-up four years ago, started their World Cup campaign with a goalless draw against a well-drilled Morocco at Al Bayt Stadium.
Only four players from their final defeat by France in 2018 started this game and they lacked an attacking spark throughout, but came closest through Nikola Vlasic's toe-poked effort.
Morocco were impressive, but failed to create clear-cut opportunities.
Belgium play Canada in the other Group F game at 19:00 GMT on Wednesday.
Croatia, who are 12th in Fifa's world rankings, dominated possession as expected, but they were unable to create opportunities or break down Morocco, who have only lost two of their past 40 games across three years.
The best chance of a match that had only two shots on target from each side came in first-half stoppage time, when a left-wing cross was diverted towards goal by Vlasic, but the midfielder on loan at Torino from West Ham was denied by the right leg of Yassine Bounou, who spread himself to close down the angle.
Morocco, who are ranked 22nd, came closest when Noussair Mazraoui followed in a deflected shot and saw a back-post header saved.
Paris St-Germain full-back Achraf Hakimi also tested Dominik Livakovic, but the Croatia keeper dealt with his dipping, swerving 35-yard strike with ease.
It was a game largely played in the middle third of the pitch, with both sides potentially wary of losing and damaging their chances of progressing to the knockout stages from a group that also contains Belgium and Canada.
The goalless draw is the third of this World Cup, after Denmark's opener against Tunisia and Poland v Mexico on Tuesday. There was only one in the entire 2018 tournament in Russia.
Croatia will play Canada in their next match on Sunday (16:00 GMT kick-off), while Morocco face Belgium on the same day (13:00).
Player of the match
HakimiAchraf Hakimi
Morocco
Squad number2Player nameHakimi
Squad number7Player nameZiyech
Squad number3Player nameMazraoui
Squad number19Player nameEn-Nesyri
Squad number6Player nameSaïss
Squad number4Player nameS Amrabat
Squad number5Player nameAguerd
Squad number25Player nameAttiat-Allah
Squad number9Player nameHamdallah
Squad number11Player nameSabiri
Squad number15Player nameAmallah
Squad number16Player nameEzzalzouli
Squad number8Player nameOunahi
Squad number17Player nameBoufal
Squad number1Player nameBono
Croatia
Squad number10Player nameModric
Squad number4Player namePerisic
Squad number22Player nameJuranovic
Squad number8Player nameKovacic
Squad number9Player nameKramaric
Squad number20Player nameGvardiol
Squad number11Player nameBrozovic
Squad number1Player nameLivakovic
Squad number13Player nameVlasic
Squad number6Player nameLovren
Squad number19Player nameSosa
Squad number15Player namePasalic
Squad number7Player nameMajer
Squad number18Player nameOrsic
Squad number14Player nameLivaja
Line-ups
Morocco
Formation 4-3-3
1Bono
2Hakimi5Aguerd6Saïss3Mazraoui
8Ounahi4S Amrabat15Amallah
7Ziyech19En-Nesyri17Boufal
1Bono2Hakimi5Aguerd6Saïss3MazraouiSubstituted forAttiat-Allahat 60'minutes8OunahiSubstituted forSabiriat 82'minutes4S AmrabatBooked at 78mins15Amallah7Ziyech19En-NesyriSubstituted forHamdallahat 81'minutes17BoufalSubstituted forEzzalzouliat 65'minutesSubstitutes
9Hamdallah10Zaroury11Sabiri12Mohamedi13Chair14Aboukhlal16Ezzalzouli18El Yamiq20Dari21Cheddira22Tagnaouti23El Khannouss24Benoun25Attiat-Allah26JabraneCroatia
Formation 4-3-3
1Livakovic
22Juranovic6Lovren20Gvardiol19Sosa
10Modric11Brozovic8Kovacic
13Vlasic9Kramaric4Perisic
1Livakovic22Juranovic6Lovren20Gvardiol19Sosa10Modric11Brozovic8KovacicSubstituted forMajerat 79'minutes13VlasicSubstituted forPasalicat 45'minutes9KramaricSubstituted forLivajaat 71'minutes4PerisicSubstituted forOrsicat 90'minutesSubstitutes
2Stanisic3Barisic5Erlic7Majer12Grbic14Livaja15Pasalic16Petkovic17Budimir18Orsic21Vida23Ivusic24Sutalo25Sucic26JakicReferee:Fernando RapalliniAttendance:59,407Live Text
Match ends, Morocco 0, Croatia 0.
Second Half ends, Morocco 0, Croatia 0.
Marko Livaja (Croatia) wins a free kick on the left wing.
Foul by Selim Amallah (Morocco).
Marcelo Brozovic (Croatia) wins a free kick in the defensive half.
Foul by Abdessamad Ezzalzouli (Morocco).
Luka Modric (Croatia) wins a free kick in the defensive half.
Foul by Hakim Ziyech (Morocco).
Foul by Borna Sosa (Croatia).
Hakim Ziyech (Morocco) wins a free kick in the defensive half.
Substitution, Croatia. Mislav Orsic replaces Ivan Perisic.
Josip Juranovic (Croatia) wins a free kick in the defensive half.
Foul by Yahya Attiat-Allah (Morocco).
Substitution, Morocco. Abdelhamid Sabiri replaces Azzedine Ounahi.
Substitution, Morocco. Abderrazak Hamdallah replaces Youssef En-Nesyri.
Foul by Josko Gvardiol (Croatia).
Achraf Hakimi (Morocco) wins a free kick in the defensive half.
Hand ball by Selim Amallah (Morocco).
Substitution, Croatia. Lovro Majer replaces Mateo Kovacic.
Sofyan Amrabat (Morocco) is shown the yellow card for a bad foul.
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