THERE SHOULD BE a warning before all U.S. youth national teams games.

Not for those with heart conditions or blood pressure-related disorders. Chronic overexposure may lead to hyperactivity and extreme mood swings.

After 18 long and grueling months of preparation, the U.S under-20 men’s national team opened up the 2015 FIFA under-20 World Cup with a 2-1 win over Myanmar early Saturday morning. After conceding early in a panic-inducing start, goals from Maki Tall and Emerson Hyndman capped the comeback win for the Americans, who now sit alone atop of Group A at the conclusion of Match Day 1.

Despite the certified underdog status of Myanmar, the plucky Southeast Asian nation took the U.S. to the limits throughout a nervy 90 minutes. It wasn’t always pretty but, at this stage, a win is a win for the under-20s, which secured its first World Cup win since 2009.

From the opening kick it was apparent that Myanmar was not intimidated by the physically imposing Americans. Displaying similar work rate to those CONCACAF minnows eager to upset the Yanks, the White Angels showed their devilish side to the shell-shocked Americans in opening quarter hour.

Looking extremely nervous the U.S. struggled to string together simple passes, with Myanmar—enjoying a partisan crowd—spending several minutes in the American half, earning more than one dangerous free kick. A goal felt inevitable.

In the 9th minute, goalkeeper Zack Steffen bungled a clearance on a corner kick, allowing the ball to fall to the feet of midfielder Yan Naing Oo, who gave Myanmar an early, shocking lead.

Just as it did during AFC qualification, Myanmar displayed an extremely high line of confrontation, keeping the Americans from establishing any sort of early rhythm and forcing a series of low-percentage long balls. The Americans' poor midfield spacing didn’t’ help matters. In one disconcerting scene, centerback Matt Miazga passed back and forth with Marky Delgado before hitting a 50-yard long ball to a line of seven Americans trying to beat Myanmar’s onside trap. It didn’t work.

After the initial round of nerves wore off, first-half chances for the U.S. came mostly in the form of—you guessed it—set pieces. In the 17th minute, the U.S. was finally able to capitalize. Off a corner kick from Hyndman, centerback Cameron Carter-Vickers flicked a header to the feet of Maki Tall who converted on the far post with an acrobatic strike to level the score.

The goal sparked a renewed vigor in the U20s, and the team quickly ratcheted up the defensive pressure, forcing Mynamar to work harder to maintain their edge in possession. With the increased physicality, the remainder of the first half devolved into a war of attrition with several rough challenges from each side and no real scoring chances to speak of—besides an audacious bicycle kick attempt from Rubio Rubin in the 43rd minute that would’ve made a few highlight reels.

After the break, the Americans looked much more comfortable. Producing a couple of nifty pass sequences, the U.S. attack regained its composure early and almost immediately put Myanmar on the back foot.

The best chance to that point came in the 53rd minute when, after a quick restart, Rubio Rubin squared an inch-perfect ball across the face of goal to a sliding Kellyn Acosta, who somehow pushed his effort wide on what should’ve been the go-ahead goal.

The Americans were aided on the comeback trail by a series of tactical changes from head coach Tab Ramos. Only minutes into the half goal scorer Maki Tall—probably the best American player in the opening 45—inexplicably made way for Los Angeles Galaxy’s Bradford Jamieson IV. The match also saw the highly anticipated American debut of Gedion Zelalem. Coming in for a departing Joel Sonora, the Arsenal reservist steadied the midfield with an incredible ease on the ball.

The moves would pay dividends. Off a 2v3 counter attack, the imposing Jameison was able to drag all three defenders, allowing Rubin to play distributor and find Hyndman on a secondary run, who cooly slotted home the eventual game winner in the 56th minute.

From that point it appeared the American had the match all but won, keeping Myanmar at arm’s length and limiting its offensive chance to long free kicks for a large portion of the second half. However after a few nervy clearances in the U.S. box, the White Angels caught a strong second wind, making hearts jump among U.S. supporters who have seen this show before.

Myanmar nearly equalized in the 82nd minute during another scramble in the box. Seven minutes later the Americans caught a massive break when goalscorer Oo whiffed on an open shot from 15 yards out.

Despite the shaky final 10 minutes, the U.S. expertly killed off the match, keeping possession for all but 30 seconds of stoppage time. Tommy Thompson nearly adding a third U.S. goal in the game’s dying seconds.

The Americans will enter Tuesday’s match with host-nation New Zealand (3am ET, Fox Sports 1) knowing that a win will go a long way toward securing passage into the knockout round. The All Blacks drew 0-0 with Ukraine earlier in the day.

ASN Contributing Editor Josh Deaver is a former academic turned soccer obsessive. Follow him on Twitter.