Will the Alex Morgan injury overshadow a perfect group stage for the United States?

Alex Morgan, who has five goals in this year's Women's World Cup, did not play in the second half against Sweden after suffering an injury. Maddie Meyer - FIFA/FIFA via Getty Images

LE HAVRE, France -- The U.S. made sure to remind its tournament competitors that the most difficult path is the one that runs through the world's top-ranked team and defending World Cup champions. But in doing so, the U.S. will have a more difficult path moving forward.

With a 2-0 win against Sweden on Thursday -- the team that eliminated the U.S. from the 2016 Olympics -- the U.S. wrapped up Group F with three wins in three games. For the first time ever, the U.S. completed the group phase without conceding a goal. (Germany also accomplished that feat this year.)

Sweden made numerous changes to its lineup heading into this game, although without removing most important pieces. The U.S. went back to its primary lineup. But if the teams approached the game with different motivations, the Americans certainly came away with theirs fulfilled after Lindsey Horan put them ahead in the third minute and Tobin Heath forced an own goal with a close-range shot early in the second half.

The prize for such success, of course, is a possible quarterfinal meeting in Paris against host and pre-tournament co-favorite France. The French also won all three games in group play. But before worrying about one of the toughest tickets in the history of the sport, the U.S. first returns to Reims, where it opened the tournament, for a knockout game against Spain (Monday, noon ET).

Those two teams played for the first time ever this past January, in Spain, with the U.S. bouncing back from an earlier loss in France to record a 1-0 win. Here are a few more takeaways:

The Alex Morgan mystery

For all the positives Thursday night and the ribbon it put on group stage success for the U.S., there was also a problematic loose end in the health of forward Alex Morgan, who suffered a hard foul late in the first half and was slow to get to her feet. She appeared uncomfortable trying to walk off the knock. Morgan was replaced at the start of the second half by Carli Lloyd.

Morgan walked through the mixed zone after the game without an obvious limp but declined to speak to the media, which left coach Jill Ellis to address the status of a player who has been in some of her best form over the past two years but has also battled injuries.

"Alex took a knock in the first half," Ellis said. "And I just think it was more of, 'Let's be smart about this' in terms of what we did."

As was the case four years ago, the Morgan watch now becomes part of the World Cup story.

U.S. knockout punch is fearsome

There is no stretch of minutes during a game in which it is easy to play the United States, but the opening 15 minutes must be particularly daunting for opponents. At its best, and certainly in each of its three games in group play, the U.S. starts games with roughly the same intensity as water out of a fire hose. That remained the case Thursday despite a much higher caliber of foe.

From a set play off the opening kickoff that nearly sprang a look at goal to barely letting Sweden connect multiple passes or break out of its own half, the U.S. swarmed and made the opening quarter of an hour largely one-way traffic. Horan's goal was the immediate reward.

"Just trying to be relentless come the first 15 minutes," Abby Dahlkemper said. "I think that's really important, to kind of put teams on their backside and be like, 'Wow, this team is really flying.' I think everyone is as fit as they've been in four years, and I think everyone is kind of hitting their stride at the right time."

Sweden doesn't make U.S. pay for missing Julie Ertz

Julie Ertz didn't start for the U.S. She was held out for what a team spokesperson described as precautionary reasons related to a hip contusion. The team didn't say when Ertz sustained the injury or whether she would have been available for the previous game against Chile, when Ellis didn't start her or most of the first-choice players. Ertz had participated without apparent difficulty in the limited portion of training open to media in recent days, including Wednesday.

In contrast to Morgan, Ertz did stop with the media after and made it clear she thinks she'll be ready for the game against Spain.

Her return creates an interesting decision for Ellis, who hasn't had to choose between her four primary midfielders yet. Sweden couldn't sustain enough possession or enough of an attack, even in transition, to make the U.S. feel Ertz's absence as a one-woman defensive clean-up crew. Instead, Horan played the position with an attacking mindset and was free to orchestrate the offense and send pinpoint passes all over the field. If Ertz returns against Spain and Horan moves higher in the midfield, it leaves a choice between Sam Mewis and Rose Lavelle -- both of whom have looked entirely comfortable in their first World Cups.

The back line debuts

After two games in which the back line spent as much time in the opponent's half of the field as defending their own goal and goalkeeper, Alyssa Naeher had little to do. That changed a little Thursday as Sweden showed some offensive prowess. While the attacks rarely amounted to much more than half chances, the U.S. was stretched at times defensively. Naeher did her part on the handful of shots and crosses that strayed into her real estate, but not all of her work is that easy to see as she settles into her first World Cup as a starter.

"She's really commanding us defensively," Mewis said. "I thought she did a great job of finding me from goal kicks or from when she had the ball at her feet and I was able to flick a lot of those on. Just her distribution has been great. She's a big transition piece for us. I just hear her commanding everyone on set pieces. I think she's had a great presence."

Inefficiency creeps into U.S. attack

Other than Horan's goal, the U.S. had two more shots on goal in the first half -- the same number as Sweden. The number that tells the difference, though, is that the U.S. put eight shots off target, while Sweden had only one. The story stayed much the same in the second half. The U.S. dominated possession and opportunities, but it didn't do much to test Swedish goalkeeper Hedvig Lindahl.

Plenty of Americans can score from outside the box, and one of the shots on target came on a well-struck low drive from Mewis, but there was a distinct sense of settling for some shots from long range against a more potent defense than Thailand or Chile.