The Qatar World Cup saw its first major upset on Tuesday as Saudi Arabia stunned Lionel Messi's Argentina in the Group C opener.
And Group E gets started on Wednesday, with the potential for further shocks as Germany and Spain bid to make winning starts.
There is also intrigue in Group F, where Canada return to the World Cup in a pool that includes two of the four semi-finalists from the 2018 tournament.
Here, with the help of Opta data, Stats Perform makes some key predictions ahead of another busy day of action.
All times local.
Morocco v Croatia – Al Bayt Stadium (1300)
Croatia were finalists four years ago, but few appear to expect them to repeat that feat in Qatar. This match may give a clear indication as to their chances of a deep run, given Croatia have lost three of their five opening World Cup games but reached at least the semi-finals in the other two tournaments.
They would appear an obvious pick to win this time, given Morocco have come out on top in only one of their past 10 World Cup matches – that a 3-0 success against Scotland in 1998.
Croatia have no shortage of experience at this level, with Luka Modric is in line to become the first player to appear in both a World Cup and a European Championship in three different decades. His exploits in 2018 earned him the Ballon d'Or, and he remains highly influential.
Player prediction – Ivan Perisic to score or assist: Perisic is now 33 and may well be playing his last World Cup, providing one final opportunity to surpass Davor Suker as Croatia's leading scorer at major tournaments. Both have netted nine goals. His 14 goal involvements are already a national record, while only Cristiano Ronaldo can match Perisic in scoring or assisting at the past five World Cups or European Championships.
Best bet – Croatia to win to nil: This will be Croatia's third World Cup match against African opposition, and they have kept clean sheets while winning the previous two, defeating Cameroon 4-0 in 2014 and Nigeria 2-0 in 2018.
Germany v Japan – Khalifa International Stadium (1600)
Germany may have bowed out early in Russia, but that was very much a rarity. Since they last failed to qualify for the tournament in 1950, that was the first time Germany had been eliminated in the first round, and they will not be looking to befall the same fate again.
Expect a fast start then for a team with a blend of youth and experience. Those older heads are used to going far at World Cups, with Germany having reached the semi-finals a benchmark four times since the turn of the century.
Japan have been highlighted as potentially tricky opponents, yet their record against European sides at World Cups is far from impressive. They have failed to score in five of their past seven such matches.
Player prediction – Takumi Minamino the man for Japan: Although Japan have not enjoyed themselves against European opposition, they had a standout performer in qualifying in Minamino, the Monaco attacker who scored 10 goals and continues to perform better for his country than for his club.
Best bet – Germany to score big: Whether Japan score or not, expect Germany to. They have not had a goalless draw at the World Cup in a record 50 matches, and only Brazil (21) have scored four or more goals in more finals matches than Die Mannschaft (19).
Spain v Costa Rica – Al Thumama Stadium (1900)
Spain and Costa Rica will have a keen ear out for how the first match in Group E finishes ahead of their meeting, with La Roja in particular heading to Qatar with lofty ambitions.
They have reached the semi-finals only once in their past 13 World Cups – en route to taking the title in 2010 – but Luis Enrique's first major tournament run at Euro 2020 took his country to the last four.
Spain face a Costa Rica side on their worst winless run at a World Cup, spanning six matches, but that sequence has to end at some stage...
Player prediction – Ferran Torres to score anytime: Unlike Spain teams of the past, there is no obvious standout goalscorer in Luis Enrique's squad. However, in qualifying, Torres was their go-to man, leading the way for both goals (four – at least two more than any team-mate) and shots (19).
Best bet – Costa Rica could stun Spain: Of course, Costa Rica's recent World Cup record is miserable, but their fans do not need to have long memories to recall past upsets. Immediately before this barren run, Los Ticos shocked both Uruguay and Italy in 2014. The win over Uruguay was one of three in Costa Rica's five World Cup opening matches, while Spain have lost seven of theirs – a record they share with Mexico.
Belgium v Canada – Ahmed bin Ali Stadium (2200)
Canada are back at the World Cup after 36 years away, although they could scarcely have been handed a tougher first test, taking on Belgium in their opener.
Coach John Herdman does at least have some World Cup experience, as he prepares to become the first coach to take a team to both the men's and women's tournaments, but that pales next to Belgium's exploits.
The Red Devils are unbeaten in their past 12 group-stage matches, winning the most recent seven in a row, and another success against Canada would match Brazil's record sequence of eight straight victories. Belgium were the leading scorers (16 goals) at the 2018 finals, too.
Player prediction – Long-shot Lois Openda to score: Openda is unlikely to start, with Michy Batshuayi the preferred option in Romelu Lukaku's absence, but he did score from the bench in Belgium's pre-tournament friendly. Given Lukaku has scored 11 major tournament goals since 2014, the Red Devils clearly create enough chances to give Openda the platform to be a star.
Best bet – Belgium to win to nil: Canada did not score in any of the matches they lost in 1986 and are one of only four teams – along with Trinidad and Tobago, Zaire and China – to play three or more matches at a World Cup without netting. That does not bode well against a team as good as Belgium.