Our expert bloggers will give their thoughts ahead of each game, so as Spain take on Chile in Group B, Rob Train (Spain) and Angus McNeice (Chile) are your guides.
What's at stake?
Rob Train: Up-and-coming sides always enjoy a chance to stick it to the top dog, so 2010 champion Spain will have to contend with a Chile team that will have the whiff of Friday's blood in its nostrils in the Maracana. Failure to win the game will, barring a miracle, spell an early exit for Spain and the ignominy suffered by France in 2002 of going out in the group stage as holders -- although Australia showed a few encouraging signs in their opener and might give the Netherlands a bit of a game. After the Clockwork Orange dismantled Spain's long watch at the top of the pile last week, the whole country will be expecting a reaction, and so will displeased coach Vicente del Bosque.
Angus McNeice: As was the case in 2010, Chile go into a group stage showdown on Wednesday with the ability to end Spain's World Cup campaign, though this time around there is so much more at stake.
At the previous World Cup, Chile had effectively secured a spot in the round of 16 before defeat in Pretoria. This year, a loss to Spain at the Maracaná would put the pressure on against a frightening Dutch side while a win would see Chile through at the expense of the defending champion.
There is also the perspective that it's now or never for La Roja. While Spain's golden era is coming to an end, the greatest generation of Chilean footballers has assembled in Brazil at the peak of its powers. With the exception of Alexis Sanchez, all the players who screamed into the U20 World Cup semifinal in 2007 will be in their 30s by Russia 2018. The stage is set for a desperate and passionate encounter.
RT: Changes are inevitable after Spain's worst showing in over 50 years, and I fancy Pedro to come into the starting lineup. The Barcelona forward's energy and application in tracking back will be vital against a side that pours forward as Chile do. Jorge Sampaoli's team played a version of 2-3-5 against Australia, and in a 2-2 draw with Spain in Seville in September, the Argentine coach deployed a 5-1-4. Jesus Navas was used then to counter the Chileans' pace, and Pedro is the next best thing in the Manchester City winger's absence. Pedro has a decent scoring record for Spain and is a better bet than David Silva to get in behind the opposition defence while also providing cover for whoever plays at right back.
AM: Sanchez has scored one and created six of Chile's last eight goals. He's obviously the team's most dangerous player. That said, Spain must be wary too of Eduardo Vargas.
The rapid Valencia man lives to turn off the shoulder of his marker and is just the kind of swift attacking nuisance Spain hate to play against. While he has struggled at times with his club form, Vargas always seems to deliver for La Roja, scoring 12 times in the last 16 international matches. The player failed to net against Australia and will be eager to break his duck in this World Cup.
RT: Sanchez. Chile's most-capped player and highest scorer helped himself to a goal and an assist against Australia and consistently performs wonders for his country. It seems incredible that Sanchez is being linked with a move from Barcelona this summer, and he will relish the chance to remind his teammates what they will be missing if he does leave. Sanchez sometimes slips out to the right and turns provider, as he did against Northern Ireland and Egypt during pre-tournament friendlies. His lethal understanding with Vargas is Chile's cutting edge.
AM: From front to back, Spain are capable of inflicting damage, though Chile will be dreading the opposition's tall timber.
As predicted, a pronking Tim Cahill easily overcame Chile's compact back line; Gonzalo Jara and Gary Medel must be having nightmares of Sergio Ramos jogging up the pitch for set pieces.
The defender nodded home in clutch moments toward the end of Real Madrid's victorious Champions League campaign, and while Chile will aim to fight fire with fire in midfield, the team is bereft of answers in this aerial mismatch.
RT: Spain's central defensive partnership against Chile's front line. Ramos and Gerard Pique were pulled apart by the Netherlands pairing of Arjen Robben and Robin van Persie, beaten for pace and dragged desperately out of position as attack after attack looked like it would end in a goal. They are not going to get a respite in Rio. How Ramos and Pique respond to the onslaught will determine the outcome of the game. Happily for Spain, reports in Chile suggest that Sampaoli is going to revert to a 3-5-2, leaving out either Arturo Vidal or Jorge "The Wizard" Valdivia. But that will still leave Charles Aranguiz to link up with the front players when Chile go on the attack.
AM: Regardless of contrasting results in their opening matches, Sampaoli and Del Bosque have both hinted at the need for changes going into this game. The Chile manager is tipped to bring midfielder-cum-defender Francisco Silva into the mix and rotating out Valdivia, who faded badly after netting against Australia.
Such a move would hardly make Spain sweat, while in contrast the rapid and dynamic Pedro shifting in for David Silva is a terrifying prospect -- especially for Eugenio Mena.
Historically capable in his usual role, Mena struggled against Australia to fulfill the exhausting double duty the manager demands of his wing-backs. He will have to summon his greatest form to assist the lumbering Jara in containing the Barcelona attacker and then transition into the pressing role that typifies Sampaoli's Chile.
RT: Pain. Chile won the game in the first 15 minutes against Australia but tired later. They will be out of the blocks quickly again. Spain looked lethargic and disjointed against the Netherlands, and I fancy Chile to do a Clubber Lang and deliver the knockout blow 2-1.
AM: The last time these two teams met was in a 2013 friendly when an injury-time goal from Jesus Navas salvaged Spain a 2-2 draw. A similarly high-scoring game is in the cards as Spain have no choice but to attack and Chile know no other way.
I bet with my head in the last 50-50; now it's time for the heart. Chile 3-2 Spain.