MEXICO CITY — As soccer players battle in the heat of Brazil, supporters raise their glasses, shout and sing passionately in homes and bars from Brownsville to Boston, San Diego to Springfield.

However, millions of these fans are not cheering on the red, white and blue shirts of Team USA, but the green of Mexico — which confronts World Cup host Brazil on Tuesday (3 p.m. Eastern time).

Mexico’s squad, known as El Tri, has proven to be the best supported national soccer team in the United States, at least in terms of game attendance.

Mexico’s three pre-World Cup friendly matches played in the US attracted a combined 191,000 spectators — compared with 103,000 at the three games of the US men’s national team.

The most popular game was Mexico-Ecuador, in which more than 80,000, overwhelmingly in dark green shirts, took to the AT&T Stadium in Arlington, Texas.

“We can fill out stadiums all over the United States. And the numbers are matched with passion,” says Sergio Tristan, from Austin, Texas, who last year founded a Tri fan club called Pancho Villa’s Army to galvanize this massive support.

In Mexico-US games with open tickets, support for Mexico is also two or three times that of the “home” team, Tristan says.

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Much of this disparity can be explained by the long-running challenge of making US sports fans take soccer more seriously.

Bumper crowds of course watch the big three sports of American football, basketball and baseball, where the nation’s best athletes play.

While soccer mania engulfs Latin America and Europe during the World Cup, some in the US don’t even know their country has a team playing.

However, the support for the Tri also speaks to the US identity as a country of immigrants. Many Americans cheer on Italy, Portugal or Russia because of their roots.

High school student Mellany Quiroz, who watched Mexico play Peru at Candlestick Park in her hometown of San Francisco last year, says she inherited the love for El Tri from her father, an immigrant from the state of Oaxaca.

“My dad was always saying, ‘Go Mexico, go Mexico!’ So I grew up supporting the team,” Quiroz says.

“At the games, there is a lot of atmosphere and fans singing,” she says, reciting the Tri anthem, “Cielito Lindo,” a Mexican folk song that’s also a mariachi favorite.

Andrea Garcia, an immigration lawyer who watched Mexico beat Cameroon at a Los Angeles bar packed with Tri fans, says the sport gives people a chance to freely connect with their heritage.

“It is one of the main ways that people feel comfortable expressing their Mexican-ness,” says Garcia, who is originally from Kansas City. “In many areas of life, it is seen badly to show your Mexican roots. But for soccer games you can wave flags and paint your face without problems.”

Divided team devotion has provoked discussion over the nature of multicultural societies in some countries. In Britain, conservative politician Norman Tebbit once called for immigrants to take the “Cricket Test” — in which the team they support shows where their loyalties lie.

However, Tristan, who served in the US military in Iraq, says such ideas are nonsense.

“We are a society with a mixed heritage and that is a good thing. Many don’t know that the United States does not even have an official language,” says Tristan, whose parents emigrated from San Luis Potosi in central Mexico.

Tristan also complains that the US men’s team has failed to capitalize on the Latino support or its talent. There are only three Latinos in the 23-man US squad.

“The team doesn’t represent me. The influential people in US soccer look to the European game and favor strength and size, instead of skill and finesse,” Tristan says.

When Tristan was younger, he says, a US trainer told him he was too short to play, ignoring the success of Latino stars such as Argentine Diego Maradona, who at 5 feet 5 inches competes with Brazil’s Pele for the title of best soccer player ever.

Support for the US team, however, does appear to be growing, with a fan club called American Outlaws opening chapters across the nation.

John Powell is among fans traveling to Brazil to cheer on the US team against Ghana, Germany and Portugal.

Originally from Erie, Pennsylvania, Powell only became a soccer fan while living in Mexico, where he coaches basketball at a school in Mexico City.

“I came to Mexico and saw the passion for the game and, when I went back to the United States, I began to get behind our team,” he says.

Powell believes the love for the Mexican team is a positive thing that could encourage more Americans to follow soccer.

“You have a game in Boston, with thousands supporting Mexico and thousands supporting Portugal. That is great for the sport,” he says. “I know a lot of people won’t agree with me, but then they don’t have an international perspective.”