Defending Olympic champion Brazil had beaten Saudi Arabia 3-1 earlier in the day to progress as Group D winner and will take on Egypt in the last eight.
A group of Brazil players showed up at the Saitama stadium to watch the encounter between their rivals Argentina and Spain and were delighted with the outcome.
Aston Villa's Douglas Luiz uploaded a video on Instagram stories in which he and his teammates Richarlison, Reinier and Matheus Cunha are all seen smiling and waving goodbye while watching the game unfold with the caption: "Goodbye little brothers."
Luiz and Richarlison were part of Brazil's squad that lost 1-0 against Argentina in the Copa America final on July 10 at the Maracana stadium.
The win in Rio gave Argentina their first major title in 28 years and saw captain Lionel Messi clinch his first major crown with the national team after four failed attempts.
Argentina won gold at the Olympics in 2008 with Messi in that squad but have not reached the podium since.