With so much riding on this game for both the USA and Portugal, the US Men’s National Team couldn’t have picked a better time to play a demoralized and injured Portugal team. But nothing is easy in soccer.

Here are 4 key match-ups to keep your eyes on during the game:

1. Cristiano Ronaldo v. Fabian Johnson

Ronaldo will play. A lesser player may have sat (if reports that Portugal’s team doctor has told Ronaldo he’s risking his career by playing on are true) but Ronaldo lives to play for Portugal.

International soccer is of the utmost importance to Cristiano Ronaldo. Perhaps that attitude is one of the only things to fully respect about the Real Madrid star.

But although Ronaldo would never miss this game, he might not be at full fitness. Ronaldo has been dealing with a knee injury since the end of the club season, and he was — by his level — ineffective in both the UEFA Champions League final and the Germany game last Monday.

However, as Luis Suarez showed against England, a great player can make great plays even short of 100% fitness. Ronaldo will start wide left, but he’ll be eager and anxious to pick up the ball early and often in this game – which means we could see Ronaldo drift.

We’ve seen all the big stars – except Ronaldo – have big moments at this tournament. Ronaldo knows how important this game is for his legacy, brand, and country. He’ll be eager to assert himself.

That means Fabian Johnson will need to be very wary. Against Ghana, Johnson fell asleep for a split-second that allowed Andre Ayew to skate past him for the equalizer. Johnson is a better attacker than defender, so it’ll be crucial that is fully aware of where Ronaldo is on the field as to not be exposed.

Jurgen Klinsmann will want to get the German-American up the field more than he was against Ghana, as it’s been suggested that Johnson is one of the American’s best attackers. The US should have more possession against Portugal than they did against Ghana, which should allow Johnson more opportunity to get forward.

2. Clint Dempsey v. Portugal Center Backs

Portugal’s problems start with their defense. Paulo Bento’s first-choice defense can be leaky and lazy to start with – hence shootouts with Israel and Northern Ireland in qualifying – and Portugal could be without three of their four first-choice defenders.

Their two best – Pepe and Fabio Coentrao – are out, suspended and injured respectively. Bruno Alves was held out of training on Saturday with a muscle problem, and is questionable at best for the game against the US.

We’re most likely going to see Ricardo Costa and Neto – two players with no major championship experience – start, possibly alongside Andre Almeida if Alves can’t go. That’s a potential gold mine for Clint Dempsey.

The Texan runs around now – almost a week after that crazy night in Natal – with a swollen and slightly crooked nose and one straight line of gash beneath his left eye. Dempsey will play, and Dempsey will be great.

One of the reasons the US have done well in World Cup tournaments recently is because their big players play well in big games. Dempsey is the big player now in many respects. He’s in the best form of his life. He’s up for a big day.

The question is, who will partner Dempsey in attack. The choice appears to be Chris Wondolowski – a gritty poacher – or Aron Johnannsson – a skillful, slender forward – but those two are both second forwards who won’t be their most effective playing with Dempsey.

It’s worth noting that when Dempsey was a late scratch from the US’ first warm-up game against Azerbaijan. Wondolowski replaced him.

We’ll see if Klinsmann trusts him again. Jurgen could also opt to change formation or move Dempsey around, if he wants to play another winger in Graham Zusi and push Jermaine Jones alongside Kyle Beckerman in the holding midfield.

Unfortunately, with the irreplaceable Jozy Altidore out of the picture for the time being, Klinsmann has flexibility. In any case, the US should want to go at Portugal’s ragged defense.

3. Michael Bradley v. Raul Meireles and Miguel Veloso

Of the myriad of surprises about the manner of the US’ opening win against Ghana, Michael Bradley playing badly in an American World Cup win stood out as chief among them.

Bradley is the formation – the only good reason why Jurgen Klinsmann switched to a 4-4-2 diamond just two months before the tournament.

He needs to play well. Really well. You wouldn’t expect Bradley, at the top of that diamond, to have two bad games in a row. He’s the man that the American attack and important possession flows through, and the curter and smarter he is with the ball, the more chances the US carves out against Portugal’s makeshift defense.

It’s up to wily veterans Meireles and Veloso to shut Bradley down and control the midfield territory for Portugal. But you have to wonder how long they’ll hold up in the inhumane heat and humidity of Manaus.

4. Joao Moutinho v. Jermaine Jones and Kyle Beckerman

Joao Moutinho is Portugal’s second best player, and with Ronaldo potentially hobbled, he needs to play well. He didn’t have anywhere near enough of an impact against Germany.

Beckerman and Jones were heroic against Ghana, with Beckerman especially shadowing and shielding the American defense and closeting and cloying the central areas.

Moutinho’s playmaking ability will be tested, and he can unlock the door, we could be in for a shootout.

Bonus: The Conditions v. Everyone

In oppressive Manaus, both teams could have problems in the second half. European teams have always struggled in heat, and Portugal’s frayed tempers and weakness for petulance may be broken if things don’t start well for them. The US has no problem with getting Portugal in Manaus. It works well for them.

But the US have had fitness problems of their own. The Americans certainly tired at the end against Ghana, and a series of alarming non-contact muscle injuries have unearthed the old saying that Jurgen Klinsmann teams are over-trained and under-coached. How will they hold up in Manaus?

A fast start will be vital in this game, because neither team may have anything for the finish.

In America, anticipation is at its highest point. No one who watched the Ghana match will miss this one, and all those who missed out on the Ghana match and heard about it for the last week will tune in as well.

This is a game in primetime on the weekend. If the US capitalizes on this opportunity, they’ll go into the knockout stages via the Group of Death, win huge respect worldwide, and catapult soccer forward again at home. No pressure then.