A Boca-Palmeiras match usually takes place later in the Copa Libertadores, but the two South American powers will go head-to-head in the group stage.
Thursday's meeting between the Argentine and Brazilian powers harks back to the days when South America's premier tournament captivated the world.
Vinicius Junior came on with a match-winning brace for Flamengo in the Copa Libertadores - and it will be just as thrilling to Real Madrid supporters.
The first week of the Copa Libertadores group stage brought surprising upsets, struggles for Brazilian clubs and the emergence of an Argentine star.
There is an inevitability to the Copa Libertadores, and that feels true once more with 16 former champions in the field, but unpredictability reigns.
The Copa Libertadores will follow the European model in 2019 and have a single final match at a host city still to be chosen.