Thursday night’s visit to Estadio Azteca (10 pm ET | FS1, Univision, TUDN) for a Concacaf Champions League semifinal first-leg clash with Club America is the type of occasion the Philadelphia Union and their supporters have been waiting more than a decade for, a game head coach Jim Curtin readily dubs the biggest in club history.

“We know it's an incredible opponent in Club America, with a ton of talent,” Curtin told reporters in a Wednesday press conference. “But our players have worked hard to get here into the final four of this competition, the top four teams on this continent. And I've asked them, dating back as early as when we played Saprissa in [the opening round of] this competition, to dream that we could eventually move on in this competition and play against the champions in Europe [at the Club World Cup]. That's our goal. It sounds like a crazy dream, but we are here now.”

It’s a moment packed with both pride and peril, a time for both heroism and disaster avoidance at an iconic venue where errors are often swiftly punished, where the best-laid plans of visitors – including generations of MLS clubs and US and Canadian national teams – all too often crumble under altitude, heat and waves of attacking pressure.

Facing one of the wealthiest and most successful clubs in Mexico, Philly know a measured but committed performance is crucial if they're to survive Thursday with a chance to win the series back home at Subaru Park in next month’s second leg.

“It's a balance, right? We have to keep things loose for the guys, so we've had fun in training, we've kept them as relaxed as possible,” said Curtin. “But then we'll also remind them that this is a big opportunity for them. When you play in a big game and you score a goal in a big game, for example, a lot of eyes come on you, and if you aspire to go to be a top player in Concacaf or be a top player in the world, playing and performing well in the biggest game is what gets you there.”

New acquisition Matheus Davo has joined the squad on this trip and is available for selection on Thursday, though Curtin stressed that the Brazilian attacker’s presence is chiefly oriented toward getting to know his new teammates and environment, noting that the game-day roster is “a tough 18 to get into right now.” The Union played a younger lineup at New England over the weekend in order to rest starters for CCL, while America are still incorporating Memo Ochoa and other players fresh off midsummer international duty and thus may be somewhat short of full strength.

Sitting amid Mexico City’s infamously polluted air at a lung-searing elevation of 2,200 m (7,200 feet) above sea level, and boasting a rich history graced by two World Cup finals on its turf, the Azteca both thrills and intimidates. The youthful Union are looking to the leadership of veterans like midfielder Alejandro Bedoya and goalkeeper Andre Blake who have been in such situations before, whether for club, country or both.

“First of all, it's impossible to be mistake-free,” Bedoya said on Wednesday. “It’s just channeling those nerves, which is perfectly normal. I think everybody should have butterflies, and once that whistle blows you just forget about everything and it's on to the game. But I think this is kind of what dreams are made out of. This is a big opportunity for every player, for our club, for the league – we’re representing the league here as the only MLS team left in the competition.

“I'm assuming that not a lot of people – similar to from the beginning, right? – are giving us a chance or don't think that we can pull it off,” he added, readily admitting that his side are marked underdogs. “But as long as we have the belief in our team, within our squad or within our players, that's all that matters. And we do have that ... We’re not a club that spends huge amounts of money on players or have that one player that can make a big difference, like some other big clubs do have. But on the field, the 11, the 18 that are dressed, we all confide in each other, and that's such an important trait to have, and that's what's brought us this far."

Philly flew to Mexico’s capital on Monday afternoon. Curtin said that the summer heat has been less pronounced than expected, and alluded to COVID-19 restrictions that will limit attendance at the hulking venue and make for a slightly less daunting atmosphere. Yet Concacaf’s tweaks to the CCL schedule may provide the most valuable boost of all, at least compared to most past MLS visitors to the “Colossus of Saint Ursula.”

This year’s tournament took a lengthy break after the quarterfinal round, allowing the Union to meet America in the heart of their season and the start of Las Aguilas’ instead of vice versa. While America are off to an undefeated start (2-0-1) to their Liga MX campaign, they’ll be further from full match fitness than Philly, a boon for the Pennsylvanians’ ability to high press with less fatigue down the stretch.

But that advantage only goes so far against such a talented adversary.

“With such strong players and a great striker like [Roger] Martinez, everybody sees how good they are going forward. But what really stood out to me is just how good they are and strong they are, and stable, defensively,” said Curtin, calling particular attention to America’s counter-pressing nous. “For me the center back, [Sebastian] Caceres, can play anywhere in the world, and there's a big reason why European clubs are looking at him to play center back. So they have a really strong team, great players. They're very well-coached, very well organized.

“We'll have to be very smart, very organized in how we approach the game. If you make mistakes in Azteca Stadium against Club America they punish you. So we have to be very disciplined, intelligent with our approach. And then survive the first 15 to 20 minutes, which is always most difficult at altitude, as you get your second wind.”