(CNN) -- The soccer bars in the United States will be jammed on Sunday. The U.S. team will play its second game of the World Cup, following a big win last Monday. Here's what to look for today from Brazil:
1. The U.S. team faces Portugal as Ronaldo returns
The United States has been, to many, one of the surprise teams of the World Cup, having pulled off a 2-1 win against Ghana last Monday.
The Americans face Portugal at 6 p.m. ET Sunday and are virtually certain to advance to the round of 16 with a win.
But Cristiano Ronaldo, not only Portugal's best player but one of the best in the world, says he'll play despite a lingering left knee injury.
That adds drama to the game and makes the United States' task much more difficult.
2. Who is Ronaldo?
He's a fast runner.
He's the best in the world with the ball.
His feet can strike left- or right-footed.
He dominates in the air.
He has skills never seen before.
That's the list of attributes U.S. goalkeeper Tim Howard ascribes to Portugal's Cristiano Ronaldo.
All eyes will be on the star player, who injured his left knee in his World Cup opening game against Germany in which Portugal endured a stunning 0-4 loss.
The U.S. team says it doesn't have a special strategy to keep Ronaldo in check. "Portugal is not only one player," said U.S. midfielder Jermaine Jones. "They have a lot of good players."
3. Watch the hair and humidity
The U.S.-Portugal match takes place in Manaus, a humid place in the jungle. U.S. coach Jurgen Klinsmann isn't too worried about the muggy climate.
"When you go through Florida and you play in Miami, it's very similar of what you're experiencing here," he told reporters at a press conference Saturday that also featured Tim Howard.
One reporter asked Howard what he thought the heat and humidity would do to teammate Kyle Beckerman's full head of dreadlocks. Howard said, "He's had that hairstyle for quite a while. He plays in the MLS, so he knows what humidity is like in the summer. I don't think it'll be a factor."
The reporter said he was doing a story about hair at the World Cup.
4. Belgium vs. Russia
Belgium hopes it will make a move toward the knockout stages if it can defeat Russia on Sunday. The teams meet at noon ET.
In its last game, Belgium sneaked past Algeria with two goals in the last 20 minutes to win 2-1. Russia played to a 1-1 draw with South Korea.
Russian goalkeeper Igor Akinfeev will be feeling the pressure. On Monday, he let a South Korean kick slip through his fingers, costing his team a chance for victory.
5. South Korea vs. Algeria
South Korea, the bronze medal winner at the 2012 Olympics, is favored to win this game, which starts at 3 p.m. ET.
Algeria doesn't have a powerful offense. In fact, the Algerians scored their first World Cup goal in 28 years in the game against Belgium.
South Korea looked lethargic against Russia, but should be able to raise their energy level.