Right-back: Danilo (Brazil)
Despite registering one assist in the competition, Brazil's Danilo has fared poorly in attack. But he has more than made up for that with stoic defending, brilliantly intercepting passes and timing his runs to perfection.
He has averaged 2.5 ground duels per game, which suggests he has been excellent in winning back possession too. Argentina's marauding wingers could have a tough time competing for the ball with Danilo.
Centre-back: Marquinhos (Brazil)
He may not wear the captain's armband for Brazil, but Marquinhos has been a real leader in defence, often seen signalling to his teammates and stepping up in crucial moments.
The 27-year-old is strong aerially, too, winning 65% of his duels. The PSG star also got on the scoresheet against Venezuela on the opening day of Copa America 2021.
Centre-back: Thiago Silva (Brazil)
Joining Marquinhos at the heart of this hypothetical combined XI is Brazil captain Thiago Silva, who continues to produce performances belying his age.
He'll soon be 37 but plays with the youthful elegance of a much younger player. The Selecao legend reads the game brilliantly and has averaged three clearances per game at Copa America 2021.
Silva has played in big games like this one before, so his experience would be crucial against Argentina on Sunday.
Left-back: Nicolas Tagliafico (Argentina)
He may not be the most menacing full-back around, but Nicolas Tagliafico has made a statement with his lung-bursting stamina and enterprise at Copa America 2021.
Tagliafico has morphed into a serious attacking player with Argentina, so Brazil will need to keep an eye on him.