A weakened Sweden team did not provide the test many expected for the US defenders. And Spain will be looking to exploit any weaknesses in the last 16

Alyssa Naeher isn’t exactly one to talk about herself. That’s why a reporter thought Carli Lloyd could fill in the gaps: what should the world know about USA’s starting goalkeeper? “I think Alyssa Naeher doesn’t want anybody to know about Alyssa Naeher,” Lloyd said, laughing.

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Naeher is USA’s first World Cup starter in goal not named Hope Solo or Briana Scurry in two decades and, although casual fans may be unfamiliar with the spotlight-shy goalkeeper now, she will eventually step out of the shadows of Solo and Scurry. Either because she will finally concede a goal in this tournament, or because she will save USA’s hide. Neither has happened yet, but with the US facing Spain in the last 16 on Monday, both those scenarios are coming into view.

Although Sweden were supposed to be the first “real” test of the US back line, the Swedes were already through to the knockout round and content to rest top players when the two teams met last Thursday. Spain, meanwhile, will be playing for their World Cup lives.

If the stats are to be believed, Spain underperformed during the group stage. Their expected non-penalty goals was around 5.5, eighth best in the tournament, but they instead scored just once from open play, according to InStat. If Spain sharpen their finishing, they could be a handful for the Americans – and for Naeher.

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Spain’s only loss in this World Cup came by a single goal to superpower Germany, and they are one of the emerging teams in women’s football. Spain won and came second in the U-17 and U-20 World Cups respectively, and there is hope that the senior side can make a leap forward of their own. What separates Spain from some other countries is that their tiki-taka, free-flowing style permeates the entire program – from the men’s side to the women’s side, at the senior level and on down to the youth teams.

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The Americans faced Spain in a friendly in January, and a narrow 1-0 win for the US shows the reigning champions cannot expect a walkover. “I wasn’t there in January when we played them but I watched on TV and I thought they were really, really good technically and really understood their relationships,” said defender Ali Krieger. “It’s going to be tough to break [them] down.”

Indeed, it is the US who may be the easiest of the two to break down. When they have faced top teams this year, they have conceded multiple goals more often than not. They are yet to concede in this World Cup, but they also haven’t been challenged much either, facing few shots on target – and those that Naeher did handle were straight at her.

Perhaps the most memorable play Naeher has made so far came in the group match against Chile when she whiffed on a ball, which allowed the South Americans to score a goal that was eventually waved offside. Naeher admitted afterward she didn’t know if it was offside and was trying to make a play. Although the error didn’t end up hurting the US, it fit neatly into a narrative questioning if the shy and reserved Naeher has a strong enough mentality to be the USA goalkeeper after the confident and outgoing Scurry and Solo dominated for so long.

Facebook Twitter Pinterest Alyssa Naeher lies on the ground after dropping a cross, which allowed Carla Guerrero to score for Chile – the goal was later ruled out. Photograph: Catherine Ivill - FIFA/FIFA via Getty Images

Even Scurry herself has raised the question. “She’s incredibly talented – she has great athletic ability and she’s very good with her feet. The only question I would have is, how is she going to perform when it’s really stressful,” Scurry told the Guardian in April. “We don’t know that.”

It was never going to be easy for Naeher to replace Solo, who holds the world record for clean sheets at international level. Solo was a superior shot-stopper and won the Golden Glove at the previous two World Cups. If Solo hadn’t been kicked off the team for being a thorn in her federation’s side, it’s a good bet that she would still be the team’s starting goalkeeper.

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But Naeher’s teammates have defended her at every turn. “Yeah,” said Julie Ertz when asked before the tournament if the questioning of Naeher is annoying. “No one’s just given her time yet. We know who she is. We train with her every single day. We know how good she is.”

The US did not concede in the group stage of this World Cup – the first time they have achieved that feat in their history. Becky Sauerbrunn hopes it will be enough to silence the critics. “I’ve thought that Alyssa has been an amazing goalkeeper for a really long time,” Sauerbrunn said. “I’m surprised it’s taken everyone else time to see it, because I see her in training day in and day out, I see her in the weight room, I see what she does, and she’s come into owning that position so much.”

The USA’s defensive problems, however, are not solely down to Naeher. On average, she’s facing more shots than Solo did during her career, and is being asked to make up for a back line that plays a far more attacking style than Solo’s defense did in 2015. Crystal Dunn, an ultra-attacking left back, conceded before the World Cup that “there are risks that are taken with the way we play” because the Americans commit so many numbers forward.

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The risk is high but so is the reward, and it has worked for the Americans so far as they continue to score at an impressive clip. They are confident that their attack-first philosophy can carry them to the World Cup final.

“It’s the cohesiveness,” Krieger said on Saturday of the US defense “Within the line, we’re constantly supporting each other and finding little things to help them improve. At half-time, it’s ‘Hey, what did you see? Can we adjust anything?’”

There hasn’t been too much to talk about through the group stage. But in the knockout rounds, of course, anything can happen.