The old enemies met in the last two finals of South America's top football tournament, with Brazil upsetting the favourites twice, but with home advantage at the July 1-24 event Argentina hope to win the trophy for the first time since 1993.
While Argentina have Messi, fast emerging as Diego Maradona's heir, at the heart of their attack, Brazil have their own brilliant player in Neymar, a potential new Pele who has already helped Santos win the Libertadores Cup at 19.
"It is our obligation to win the tournament," said Argentina coach Sergio Batista, who plays the high-scoring Messi in a roving centre forward role akin to his flexible position at Barcelona.
Argentina open the world's oldest active major soccer tournament at the modern, roofed Ciudad de La Plata stadium on Friday when they take on Bolivia in Group A.
They have a score to settle, having been thrashed 6-1 the last time they met in a World Cup qualifier at high altitude in La Paz two years ago during Maradona's time as coach.
An attack boasting Messi, Carlos Tevez and Ezequiel Lavezzi, with Gonzalo Higuain, Sergio Aguero and Angel Di Maria on the bench, should have little trouble brushing aside the Bolivians in a relatively easy group for the hosts. They also meet Colombia and Costa Rica.
Brazil, with coach Mano Menezes going back to the basics of his country's "beautiful game" after the pragmatic Dunga era, kick off against Venezuela in Group B at the same venue on Sunday before heading for Cordoba to play Paraguay and Ecuador.
Menezes' pair of aces are Neymar and his 21-year-old Santos team mate Paulo Henrique Ganso, an exquisite playmaker the coach hopes will spark Robinho, a veteran of Brazil's 2007 victory, and Alexandre Pato up front.
URUGUAY THREAT
Uruguay come to the tournament on the back of their fourth place at the World Cup and with hardly any changes in personnel or style but a fresher 32-year-old Diego Forlan after a tough season in Spain that included an alarming loss of form.
"There is a very strong [team] base around Diego Forlan [and] he is in very good physical condition [after a refreshing break]," said coach Oscar Tabarez, one of the few coaches to survive a post-World Cup cull.
Uruguay will also play a match in La Plata - an obligation for the seeded teams in the three groups - but only when they meet guest team Mexico there on June 12. They kick off Group C in the Andean city of San Juan against Peru on Monday.
Chile and Paraguay, who had good World Cups last year, especially the latter with their place in the last eight for the first time, will be tough opponents.
Colombia are dark horses, with an attack boasting Radamel Falcao Garcia, whose top-scoring exploits helped Porto win the Portuguese championship and Europa League.
"I think Colombia will have a good Copa America, a good World Cup qualifying campaign and qualify for the finals [in Brazil in 2014]," Pa
