With a close 2-1 win, the defending champion U.S. women's national team just barely advanced to the next stage of the knockout round after defeating Spain on Monday in an extremely physical and high intensity match.

USA entered the round of 16 after topping Group F with three wins, while Spain, playing in just its second World Cup, finished second in Group B. Spain entered the match already having made it further than it did in 2015 as the Spaniards were eliminated in the group stage in their last tournament appearance.

The Spaniards put the Americans to the test and brought a central midfield that was potent and hard to stop with lower pressure. The U.S. saw its first bit of adversity in the tournament and though the national team handled it well, the Americans are going to have to make adjustments heading into the quarterfinals.

The U.S. will have a few days off before facing France on Friday in Paris.  

Here are three takeaways from the USWNT's win:

The U.S. wasted an insane number of opportunities 

Plain and simple: The U.S. didn't look like itself. The Americans had a number of attacking chances they couldn't convert. They were good out wide with Tobin Heath, Kelley O’Hara, and Crystal Dunn as they combined with the central midfielders to create chances, but the U.S. couldn't convert and looked sloppy. At halftime the United States had just a 14% conversion rate, which is extremely low.

The Americans took 12 shots and just three of them were on target. Another surprise came in the fact that the Americans and Spaniards shared relatively equal ball possession. The U.S. had the ball 56%, Spain had it 44%. It was widely expected the U.S. would have complete control of the game.

While Megan Rapinoe scored USA's first goal in the seventh minute and again in the 75th off of penalty kicks, she was highly ineffective. She kept losing the ball, was questionable on some of the decisions she made and her shooting was off. 

If it weren't for penalty kicks, there's a chance the U.S. wouldn't have scored at all.

Spain put goalkeeper Alyssa Naeher to the test

Spain exposed where the USWNT needs to improve the most: in its goal. Alyssa Naeher hadn't been challenged nearly at all throughout the tournament — until Monday's match. She made two saves against Sweden, showing some promise, but made a costly mistake against the Spaniards. 

There's a lot of pressure for Naeher as she has to fill the void left by Hope Solo, the USA's safety net for more than a decade, after the 2016 Olympics. Entering Monday's game, she had a career 72% save percentage with 27 clean sheets, but she allowed the U.S. to concede its first goal of the tournament.

There was a misunderstanding between Naeher and defender Becky Sauerbrunn as Spain's Lucia Garcia stole the ball from Sauerbrunn and assisted Jennifer Hermoso, who scored her third goal of the tournament.

Hermoso's score ended a run of 648 minutes in all competitions — and 308 minutes in World Cup play — that the U.S. went without allowing a goal.

As the match went on, Naeher and the backline communicated better, but it'll have to be stronger heading in the quarterfinals as France is more dominant on attack.

The U.S. will have to step up big time against France

The U.S. colliding with France in the quarterfinals has been a storyline for much of the tournament, but Spain gave the U.S. a scare.

The Americans are going to have to play a completely different game in the quarterfinals. If they play like they did against Spain, it could easily end in elimination from the tournament. France was among the favorites entering the tournament, and Les Bleues won Group A pretty easily with a 3-0 sweep. They just barely pulled off a win against Brazil in extra time Sunday, but the Americans still will need to be at their best to advance. 

One question will be around Alex Morgan. She was subbed out in the team's group stage finale against Sweden with injury concerns, but started against Spain. She didn't look herself and took several big hits, but the Americans will need to be able to rely more on Morgan to advance past France.