With Euro heavyweights Germany and Portugal meeting first at 5pm BST, we then see Iran and Nigeria face off and Ghana and USA in action.
But away from the action, there's been a few talking points for fans and pundits alike in South America.
Neymar up for fun
Ahead of their second group match against Mexico on Tuesday, the host nation Brazil are still looking pretty relaxed off the pitch.
Brazil pair Neymar and Marcelo drag striker Fred off the pitch
Their training session on Sunday saw star man Neymar at the heart of the fun, executing a playful karate-kick on team-mate Fred, then showing off his skills by playing keepy-up with a rolled-up pair of socks before he was joined by Marcelo to unceremoniously drag Fred off the training pitch by his arms and legs.
Oh, and once he'd removed the beanie hat later, he also unveiled a new-look blond hair cut along with his Barcelona team-mate Dani Alves.
Croatia get shirty
There were different scenes at the training base of Brazil's Group A rivals Croatia, as their squad have decided to withdraw from participating in any media interviews.
This comes after a number of the squad were snapped by a posse of sneaky photographers hiding in bushes, apparently enjoying a skinny dip in their hotel swimming pool.
Croatia boss Niko Kovac delivered the bad news to reporters on Sunday
Boss Niko Kovac delivered the news to disappointed reporters on Sunday, saying: "I can’t force them to be at your disposal after what you have done to them and their families.
"How would you feel if someone took naked pictures of you? They are adamant that they won’t speak to you lot any more and I don’t know whether the silence will end tomorrow or last until the end of our World Cup campaign.
"I respect my players’ opinion and I also know that you have done a very professional job so far but you blew it with this one. The whole world has seen the photos."
GLT confusion
Whilst there was no doubt that France’s second goal against Honduras was a close-call after Karim Benzema’s shot cannoned back off the post and in off the goalkeeper, the delivery of the subsequent review via goal-line technology caused confusion for commentators around the world, fans at the stadium and also the boss of Honduras.
Honduras boss Suarez questions the goal line technology in his side's defeat against France
Luis Suarez, not the Liverpool striker incidentally, was forced to see the decision on the stadium’s big screen in Porto Alegre and reacted quickly when it showed the shot against the post as ‘No goal’ only to then reveal the second phase was over the line.
"The machine first said no [goal]. I do not know what to think," said Suarez.
"If the technology sends a clear message, then I don't understand how the system can say it's a goal first and then: 'No goal.' What is the truth?''
It was clearly a goal, Luis.
