13:00 BST, Sunday 17 June, Samara Arena (Samara, Russia), ITV
Costa Rica, who stunned both Uruguay and Italy and tied England to win their group in Brazil four years ago and ultimately reached the quarterfinals, are back thanks to a pair of wins over the United States in qualifying.
However, Los Ticos are no longer a surprise and enter the tournament amidst a rough patch.
Oscar Ramirez's side were outscored 6-1 by England and Belgium this month and also suffered friendly defeats to Tunisia, Hungary and 5-0 versus Spain since the start of November.
If the Costa Ricans aren't able to turn things around for this match, their tournament might be over before it starts.
Serbia, meanwhile, return after not qualifying for the World Cup in 2014 following consecutive group stage exits in 2006 and 2010 (the former as Serbia & Montenegro).
The Serbians won six times and lost just once during qualification, but still face a tough challenge in a group that features World Cup contender Brazil and a confident Switzerland side.
Mladen Krstajić took over as manager for Slavoljub Muslin in October, and the team went 2-1-2 in friendly competition. That small sample size wasn't all that impressive with losses to Morocco and Chile plus a tie versus South Korea.
Last Time Out
Belgium 4-1 Costa Rica [International Friendly]
The Costa Ricans took the early lead on Monday through Bryan Ruiz's goal in the 24th minute, but Belgium were the aggressor throughout as they missed some early scoring chances before breaking through on 31 minutes.
The Belgians scored again before the half and Los Ticos were trying to limit any further damage after the break.
Ramirez made five changes from the loss four days to earlier to England, but that didn't help as Costa Rica's defence against top-tier teams continues to be a concern.
Serbia 5-1 Bolivia [International Friendly]
Three goals and an assist from striker Aleksandar Mitrovic gave Serbia a much-needed productive performance after falling 1-0 five days earlier to Chile, who failed to qualify for the World Cup.
Krstajić made the move to a 4-2-3-1 formation after the Chile effort, and it paid off.
The result against Bolivia could provide the boost needed for Serbia, who totaled four goals in their previous four games. A little extra confidence might go a long way for Krstajić's bunch.
Costa Rica Lineup
While defence remains an immediate problem for Costa Rica, it's uncertain if Ramirez will make any changes at the back. Up front, Johan Venegas could be used instead of Urena, while David Guzman and Yeltsin Tejeda are also options in the midfield.
The 4-2-3-1 formation worked against Bolivia and should be incorporated in the opener, especially against a Costa Rica side who has struggled at the back. It allows Sergej Milinkovic-Savic the platform to play in a more advanced position, supported by Nemanja Matic and Luka Milivojevic.
Antonio Rukavina could also be used at the back of this lineup, but may see action even if he's not in the starting XI.
Key Battle: Sergej Milinkovic-Savic (Serbia) vs Keylor Navas (Costa Rica)
The 23-year-old Milinkovic-Savic is a star in the making and a budding commodity worldwide after scoring 12 goals for Lazio this season.
He has just three caps for his home country - perhaps one reason Muslin is no longer coaching - but the upside is tremendous.
If Milinkovic-Savic can play in line with his teammates on football's biggest stage, Serbia could seriously contend for a knockout stage spot. The Lazio midfielder has also showed his volatile side at times, so keeping his temper is a must.
Navas is coming off a third straight Champions League title with Real Madrid, but he needs to play better than he did against England and Belgium (stopping eight of 14 shots) this month. Then again, he wasn't the only one at fault.
The 31-year-old shined for Costa Rica in 2014, and it appears they will need to rely on him again, especially if their defence doesn't improve. That's a lot of pressure, even for one of the world's best keepers.
Can Costa Rica find another gear?
It can't be overstated enough how troubling their recent losses against England and Belgium were. Ramirez said after the Belgium defeat he wants to see more speed and better passing from his side.
Ruiz and Joel Campbell have the potential to provide that, but will they be able to sustain it if they do? And can anybody help?
On paper, the Costa Ricans look balanced, and that's what they must find in time for kick-off. Perhaps the memories of 2014 and the experience factor (14 players with at least 40 caps) will allow Los Ticos to flip the switch this week.
Serbia have some sneaky talent
The likes of Premier League players Dusan Tadic, Nemanja Matic and Luka Milivojevic, plus Roma's Aleksandar Kolarov, veteran Branislav Ivanović and Mitrović provide credibility to the Serbian roster, but none are superstars.
That's what Serbia lack, and a reason they are more of a dark-horse than a serious contender for the knockout stage.
However, if the sum of all their parts come together, then the best might be yet to come for a nation many don't know what to expect from in the tournament. One thing is for sure, Costa Rica should have their work cut out from the get-go.
Prediction: Serbia 2-1 Costa Rica
With Brazil the obvious Group E favourite and Switzerland good but beatable, this opener has the potential to be the most significant match in terms of the group's complexion going forward.
Don't underestimate Serbia's rout of Bolivia and the amount of confidence they generated from the victory.
That notion, coupled with Costa Rica's recent defensive issues, puts Serbia in a good position to win their first World Cup match since stunning Germany in 2010.
Listen to the RealSport football writers discuss Group E in Kremlins in the Basement: RealSport’s daily World Cup podcast.