Mexico Fans Dress Duck For World Cup, Wild Scenes From Day 1

We already have a submission for best fan of the FIFA World Cup ... 'cause this one fits the bill!!

The first day of the international soccer tournament kicked off on Thursday ... with Mexico and South Africa duking it out in Mexico City.

There were plenty of memorable moments from the 2-0 win for El Tri ... but one clip of an adorable duck supporting its favorite team is taking the cake.

A clip posted on social media shows the lil' one waddling among the humans in Mexico City ... all while rocking a Mexico jersey.

The visual is pretty tame compared to the other wild antics from Thursday -- Mexico fans flooded the streets after securing the dub ... and took to the streets to celebrate, a la New York Knicks supporters this NBA Finals.

Soccer really is the world's sport, 'cause it's bringing people from all different countries together. Mexican diehards have been hanging out with the folks in town to watch South Korea ... even soaking in their victory over Czechia together!!

They might live thousands of miles apart, but the Mexican fans found common ground by chanting "BTS" to show one Korean spectator some love.

Another got thrown into the air among a bunch of Mexico supporters ... which is really what the World Cup is all about!!

There's more where that came from ... as folks dusted off their best "Gangnam Style" dances as well.

Speaking of K-pop, aespa idols Karina and Winter actually attended the match at Estadio Guadalajara ... and they must've been good luck charms.

Mexico and South Korea is the new friendship we're here for -- but they'll be enemies next week when they face off in the group stages.