RUBIO RUBIN IS A FEARLESS and relentless striker. Midfielders Gedion Zelalem and Emerson Hyndman are great with the ball at their feet and possess plenty of offensive flair.

But the biggest asset on the United States under-20 men's national team may just be the three men tasked with keeping opponents off the scoreboard.

Goalkeeper Zack Steffen and central defenders Matt Miazga and Cameron Carter-Vickers have logged a total of 720 minutes together between U-20 World Cup qualifying and the World Cup. When all three are on the field, Tab Ramos' squad has conceded just three goals—that's one every 240 minutes.

The team will face a stiff challenge against Serbia Sunday night (12:30AM ET, Fox Sports 1) but Miazga believes the entire team is up for the challenge.

“The mood is very good on the team,” Miazga told American Soccer Now from New Zealand. “We’re all confident. We are a very talented team. I think the spirit is really high and we are all excited for the quarterfinals. We’re very proud.

"It’s been a great, great week for U.S. Soccer and we are looking to continue that in the quarterfinals.”

Miazga, 19, has enjoyed a very impressive tournament so far. The six-foot-four Clifton, N.J., native has played 270 minutes so far in New Zealand and the team has conceded just one goal with him on the field.

The New York Red Bulls product delivered his best performance Wednesday as the Americans stymied a rugged Colombia team, 1-0. In that round of 16 matchup the United States had to deal with an early injury to a starting forward Bradford Jamieson, a red card, and a very physical and determined opponent.

Colombia had more chances and more possession, but the U.S. backline absorbed the pressure and the offense took advantage of its one real chance.

“The Colombians were just like the other South American teams we played—very feisty, going into every 50-50 challenge like it was their last, and very big and strong as well,” Miazga said. “It doesn’t really matter. I definitely embrace it and I like the challenge.

"I like when big forwards come at me and are strong. It’s good when you’re a centerback and you stop play after play. I like it when I play against anyone good and you challenge yourself. It’s the world stage now and everyone you go against is going to be a really good player.”

Both in qualifying and in New Zealand, Ramos' teams have found a way to win close games—even against quality opponents who create most of the opportunities. Having a rock-solid defensive core is a key part of that.

“My partnership with Cameron is really flourishing,” Miazga said. “Our games complement each other. It showed in qualifying and now we’ve gotten some big wins in New Zealand.”

The defining moment of Wednesday's match came in the 81st minute when referee Antonio Ivan Bebek called a penalty on U.S. defender Kellyn Acosta. Colombia's Jarlan Barrera stepped up to the penalty spot with a chance to even the score, but Steffen dove to his right and stopped the low, left-footed shot.

Miazga, who has a long history with Steffen, had a feeling his friend was going to come up with the big save. The goalkeeper had produced a massive penalty save against El Salvador during World Cup qualifying.

“I’ve known Zack since I was 14 and we’ve been playing consistently for the U-18 and U-20 national teams,” Miazga said. “He’s been a great leader and an amazing teammate. With that penalty, I was honestly having deja vu. I thought right back to that El Salvador game because it was the same situation.

"I had faith in him. We’ve been practicing PKs in training and we know Zach is a great shot stopper. You had that gut feeling that he was going to save it.”

Next up will be a talented Serbian team that defeated Mexico and Mali in the group stages and then posted a 2-1 extra-time win over Hungary in the round of 16. It will mark the third straight game in which the U-20s will be face a significant size disadvantage.

Miazga like his team's chances despite the fact that the Yanks will be without two injured forwards, Bradford Jamieson and Maki Tall, and suspended players Jordan Allen and Kellyn Acosta. Before the tournament the U.S. faced off against Serbia in a closed-door friendly and while foreign reports said Serbia won 1-0, Miazga said it was an “even” game.

Serbia is likely favored but the U.S. U-20s' team effort in the win over Colombia has convinced players they can succeed against any opponent.

“Tab told us before the [Colombia] game, ‘It was the World Cup, what more do you want? You’re playing for your country and your families. It’s a huge opportunity for us and everyone will be watching,’” Miazga recalled. “We went out there and played with our hearts. We played well.

"We got the win, which is the most important thing.”

Brian Sciaretta is an American Soccer Now columnist and an ASN 100 panelist. Follow him on Twitter.