We've had our first big shock of the tournament, as Saudi Arabia beat Argentina 2-1 yesterday. It was statistically the biggest shock in tournament history, according to data company Nielsen Gracenote, but where might we see some other upsets on Day 4?
Two of the massive European nations are set to begin their World Cup campaigns, with Germany - winners on four occasions - and Spain, who lifted the trophy for the only time in 2010, both in action.
Finalists four years ago Croatia are also up, while the golden generation from Belgium - semi-finalists in 2018 - are almost certainly competing together in a tournament for the final time.
Like yesterday, there are four games today, starting at 10am and finishing up close to 10pm tonight, all live on RTÉ2 and the RTÉ Player.
Germany are set to face Japan at 1pm in Group E having lost a major sponsor yesterday over the fallout of them being one of the seven European nations to refuse to wear the OneLove armband. Their players know that there's a €400,000 bonus each available if they go on to lift the trophy next month.
Can this group add a fifth world title to the record books? Well they've brought back someone who was on the field for their last win eight years ago. Mario Gotze was been out of favour with the national team for the last five years but he's in the 26-man squad.
It's the first time the Germans have gone to a major tournament without Joachim Low in the dugout since 2004. They bid auf wiedersehen to the blazer-clad man who started out as the assistant manager when they hosted the World Cup in 2006. He led them to the 2014 title, as well as the final of Euro 2008, but moved on after their last-16 exit to England at last year's Euros.
Hansi Flick is his replacement and led Germany to top group J in qualifying with nine wins from 10 games.
It's 20 years since Japan hosted the World Cup alongside South Korea, who themselves dumped Germany out of the tournament four years ago. They've been at every World Cup since 1998, but have never gone beyond the last 16.
Veteran defender Yuto Nagatomo could pass the 140-cap mark during the group stages, with the FC Tokyo 36-year-old currently having played 138 times for his country. Closer to home, Arsenal's Takehiro Tomiyasu is recovering from a hamstring issue, while Daizen Maeda will be known to followers of Celtic.
Spain are also in Group E but this is a much younger squad they bring to the tournament as they look to recreate the golden years of 2008-2012, when they won two Euros to nicely bookend a World Cup triumph.
It's a young Spain squad, the third youngest in the competition with an average age of 25.3 years. Six of the squad are under 20 and could make their tournament debuts during the group stages.
"Youth gives you freedom because you are not yet aware of the consequences," manager Luis Enrique said of his players.
"Yet, most of the youngsters that are with us are already in high-level teams. The bar that I'm setting is infinity. My goal is to compete in every game.
"There's no one outside of Spain who rules out Spain as a candidate to be among the best. We are going to give war, there is no doubt."
Will we be seeing the dawn of a new youth-driven period of Spanish dominance?
Group F will get Wednesday's action underway, with Croatia setting out to go one better than they did four years ago. Then, they were beaten by France in the final.
The Adriatic side have only been entering World Cups since 1998, having previously been part of Yugoslavia, but they've certainly made their mark adding a semi-final spot 24 years ago to that trip to the showpiece match last time out.
"What we went through in 2018 was an unforgettable experience, indelible in our minds," said captain Luka Modric, who collected the Golden Ball award in Russia for the tournament's best player.
"Many players that were at the Russia World Cup are not here, new players have come, quality young players with fresh energy. This is a new tournament and we have to look at it that way."
The Croats impressed in qualification, recovering from defeat the first day to Slovenia to remain unbeaten in their next nine games, winning seven of them. They topped Group H ahead of Russia.
Opponents today Morocco, who are competing at their second World Cup this century, have had little time to prepare with new manager Walid Regragui coming into the job in August. Since then he's guided them to friendly victories over Goergia and Chile, as well as a draw with Paraguay.
The other game in Group F, and today's 7pm kick-off, will see Belgium take on Canada.
The narrative is clear for the Belgians; this is the last chance to do something truly memorable for the best generation the country has ever produced.
"For us the World Cup is the last chance to show that we can still win something with this generation," Eden Hazard said recently.
Kevin de Bruyne has strongly hinted that this will be his last World Cup while Inter Milan's Romelu Lukaku will miss the game with a thigh injury.
The Canadians arrive at their second World Cup, and their first in 36 years. They'll hope to do better than they did at Mexico '86 where they lost three games and failed to score. They impressed in topping their Concacaf qualifying group ahead of Mexico and the United States.
The fitness of Alphonso Davies is a big talking point, with the Bayern Munich star meeting up late with the squad as he received treatment at his club for a hamstring injury. They did managed to win half of their qualifiers without him, mind, so they'll be used to having to cope if he doesn't make it.
Eleven of the Canada squad play their club football in North America.
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