Thousands of flag-draped supporters of both sides have made the huge journey to Qatar and arguably been the liveliest presence, organising street parties and teaching Spanish-language chants to Arab fans eager to join in.
"They are the craziest and the best! This is exactly what we were waiting for," said Ibrahim Hussain, a Saudi Arabian wearing a Lionel Messi shirt, as he watched Argentines and Mexicans banter good-naturedly on the Qatari capital Doha's sea-front.
Saturday night's Group C match at the Lusail Stadium is, however, a deadly serious matter for both.
Argentina began their World Cup with a shock 2-1 defeat to Saudi Arabia in a disastrous start for Messi's fifth and final attempt to win the one big trophy that has eluded him.
Mexico, eliminated in the last 16 at the previous seven World Cups, scraped a 0-0 draw with Poland in their opener.
So both need a win to get their tournament going and match the enthusiasm of their fans.
ARGENTINE NEMESIS
"Argentina have always trod on us and they look down on us. That has to change. Today is the day to rewrite our history with them," said Guillermo Sanchez, 44, from Mexico City, sporting a wide-brimmed sombrero along with friends.
Argentina are indeed something of a nemesis for Mexico, having beaten them in all three previous World Cup encounters stretching back to a 6-3 win at the inaugural 1930 competition then last-16 victories in 2006 and 2010.
Though fans of both nations have drawn plenty of admiring attention - and endless selfies - in Qatar since the tournament started, the rivalry went too far earlier this week.
Social media videos showed Mexican fans provoking Argentines with insults over top scorer Messi and their Falkands War defeat to Britain. That led to some street brawling that left some fans bleeding and injured, according to the footage and photos.
"It's OK for the Mexicans to have a joke with us, we can take that. But they are not in the same football league as Argentina," laughed Jessica Martinez, a 33-year-old sales assistant travelling with friends from Buenos Aires.
"Remind me, how many World Cups have Mexico won? Oh yes - none! How many have Argentina won? Two for now, but three by the end of this tournament - you watch!"
