Brazil opened Group E play with a 1-1 tie against Switzerland in a disappointing tournament opener for one of the World Cup favorites. Iceland, meanwhile, is soaring after a 1-1 draw with mighty Argentina in its World Cup debut.
Iceland is the smallest nation in field and playing in only its second major tournament. The tiny country became a darling of the soccer world after its improbable run to the quarterfinals of the 2016 European Championship. A win or draw Friday in Group D play would make Iceland the first squad to avoid a loss in its opening two World Cup matches since Senegal in 2002.
But the day begins in St. Petersburg in a match between Brazil and Costa Rica. Questions surround Brazil star Neymar, who limped out of a training session earlier this week.
The Brazilian soccer federation said Thursday that Neymar is just fine and posted photos and a video of him practicing Wednesday with the rest of the squad.
"I trained well, felt comfortable," Neymar said in the video. "The foot is fine."
Brazil officials insist his current issue is not linked to the foot injury that sidelined Neymar for about three months earlier this year. Brazil needs him to deliver after the flat draw against Switzerland. The team is among the top in the world and anything but a victory against Costa Rica would make it harder to advance from the group stage.
Brazil also has a controversy over which player to start in the lone-striker role. Gabriel Jesus started Brazil's opening group game but was substituted out by Roberto Firmino, who was the stronger player and nearly scored a late winner from a header.
Costa Rica, meanwhile, topped its group and reached the World Cup quarterfinals four years ago but is on its heels after a 1-0 loss to Serbia in its first game. Costa Rica doesn't have history on its side: Brazil has won nine out of 10 matches against Costa Rica, with its only loss coming in a 1960 friendly. Costa Rica's only World Cup victory against a team from South America was four years ago against Uruguay.
The first of Friday's three games begins at 3 p.m. (8 a.m. EDT; 1200 GMT).
A look at Friday's other matches:
NIGERIA VS. ICELAND
6 p.m. (11 a.m. EDT, 1500 GMT)
Nigeria dropped its first group match 2-0 to Croatia and is considered so far to be one of the underperforming teams of the tournament.
The Nigeria team is the youngest in the World Cup with an average age of just below 26, and although it is the most populous nation in Africa with some 185 million people, the team has never advanced past the round of 16.
The game in Volgograd is so highly anticipated in Iceland that its national post office has announced it will close more than three hours early as most of the country is expected to watch.
The draw against Lionel Messi and Argentina was nearly as big as a victory and has Iceland believing it can advance out of the group. To do so, captain Aron Gunnarsson said, Iceland must forget about the Argentina match.
"We can't dwell on that game now," Gunnarsson said. "If we don't focus on Nigeria and don't get a result there, then that (Argentina) point is no use for anyone."
Iceland goalkeeper Hannes Halldorsson was the man of the match against Argentina, chiefly for saving a penalty kick by Messi.
"This is a must-win game for Nigeria, and that makes it a little bit psychologically different — they have to win," Iceland coach Heimer Hallgrímsson said. "This group is going to be decided in the last minutes, in the last game. It's going to be down to some margins, a set piece, a goal in extra time. This is how this group is going to be played."
SERBIA VS. SWITZERLAND
9 p.m. (1 p.m. EDT, 1800 GMT)
A 1-0 victory over Costa Rica has Serbia headed into its game against Switzerland eying a spot in the round of 16.
Because Brazil's opener also ended in a draw, Group E is wide open right now and Serbia will play Friday for an outright victory against Switzerland.
"If we do the math and start playing for a draw then it will not be successful," captain Aleksandar Kolarov said. "Of course we want to win."
It was a free kick from Kolarov that put Serbia in solid position in the group, but Switzerland may be as tough a foe as Brazil. Switzerland has lost just one of its last 23 matches — a 2-0 defeat to Portugal in a World Cup qualifier in October.
Switzerland used a strong defense and midfield to stifle Brazil, and midfielder Valon Behrami made the match very difficult for Neymar. Behrami became the first Swiss player to appear at four World Cups when he started against Brazil, but he left that match in the 70th minute with a thigh injury.
It's not clear how healthy he'll be for the match, and he skipped at least one training session this week.
Serbia, meanwhile, is seeking to reach the round of 16 for the first time since 1998, when it was known as Yugoslavia. The team did not make it out of the group stage in 2006 or 2010 and did not qualify for Brazil four years ago.