The U.S. women’s national team heads into Friday’s quarterfinal match against China down two key players. Here are three keys to the team advancing. (Tom LeGro/The Washington Post)

Tucked inside “the bubble,” that literal and figurative shelter in which the U.S. women’s national soccer team has retreated between matches and practices at this worrisome World Cup, players say they have blocked out biting criticism from fans fearing an embarrassingly early exit.

They say they don’t listen to former players and coaches, some with axes to grind, reminisce about the good ol’ days (circa 1999). They say they haven’t read columns and social media screeds chastising their coach’s tactics and goalkeeper’s past transgressions.

In the bubble, the Americans say, they remain upbeat about raising their quality after four unconvincing performances. But this much is clear: If the United States falls to China in the quarterfinals Friday night at Lansdowne Stadium, the fury will swell.

And there will be no place to hide.

Since FIFA launched official competition for women 24 years ago, the Americans have participated in seven World Cups and five Olympics. In the previous 11 tournaments, they have won six championships and finished second twice. The other three times, they won the third-place game.

In other words, they have never failed to reach the semifinals of the sport’s premier competitions.

“They understand we have to continue to raise our level with each round,” Coach Jill Ellis said Thursday. “It’s not a matter of being satisfied. These are players that love challenges. The coaches have high expectations, but it’s about getting to that point, so we are certainly capable of a lot more.”

This isn’t the first time the U.S. team has confronted vulnerability in the quarterfinals, though.

The celebrated 1999 squad of Mia Hamm, Michelle Akers and Brandi Chastain had to come from behind twice to overcome Germany at FedEx Field, 3-2. Four years ago, Abby Wambach’s equalizer deep in extra time stunned Brazil before the Americans prevailed on penalty kicks.

This summer, with a tight defense compensating for a sour attack, the Americans have stumbled into the quarterfinals.

The team’s overall form has drawn criticism from fans and those with deep ties to the program, most notably Akers.

Although the current crew acknowledges difficulty blocking out the digital noise, they say they are not allowing it to distract them.

At Wednesday’s media briefing, the three players available for interviews all separately referenced “the bubble.”

“We’ve done an incredible job as a team keeping our bubble intact and not listening to the media or outside criticism or outside sources,” defender Meghan Klingenberg said.

“We are all trying to stay in our bubble,” midfielder Carli Lloyd said.

“We really try to keep our bubble tight,” defender Lori Chalupny said. “We don’t let outside things get into what we’re doing.”

If distractions aren’t affecting their game, something is. And with each shortfall has come increased pressure not only to advance but to operate with greater style.

“I actually think this team performs better under pressure,” said defender Becky Sauerbrunn, a University of Virginia graduate. “We put a lot of pressure on ourselves to be the best. Every game, we expect to win, so we are used to that pressure.”

That pressure has yet to inspire better performances. In the round of 16, a fledgling Colombian side exhibited superior technical skill in much of the first half. Although the Colombians did not test goalkeeper Hope Solo, they were competitive until a red card early in the second half swung the match in the Americans’ favor.

The 2-0 victory secured passage but hardly reassured U.S. supporters, who are long accustomed to international excellence against less-established programs.

Ellis’s tactics and player selections have come under increasing scrutiny. She has leaned heavily on striker Abby Wambach, the sport’s greatest scorer who scored the winner against Nigeria in the group stage but, to many observers, has hindered the attack.

The other primary criticism is Ellis is too rigid with her alignment and hasn’t put her attacking players in position to succeed. On Thursday, she said, “Defensively we’ve been brilliant. In terms of attacking, we are creating chances. What it comes down to is we have choices around the ball, and it’s really about what choices you make.”

Forward Alex Morgan, who scored against Colombia, said: “We’re seeing moments of greatness, but we’re not seeing 90 minutes of it.”

On Friday, the Americans will play without midfielder Megan Rapinoe, the influential left wing, and Lauren Holiday, a central midfielder. Both are serving yellow-card suspensions. Morgan Brian (Virginia) will probably start for Holiday, while Christen Press is the top candidate for Rapinoe. It’s unclear whether Wambach will make her fourth start.

Although China cannot match the Americans’ experience, Ellis called it “probably one of the best organized teams in the tournament. They make it very hard to break down.”

Given the U.S. team’s attacking woes, plus Rapinoe’s absence, the Chinese are well equipped to oust the Americans and gain a touch of revenge for the 1999 final at the Rose Bowl.

“We have a new mind-set,” defender Ali Krieger said, “that the tournament is starting now.”