Doncic, a 2.01-metre (6 foot 7 inch) point guard, who led Slovenia to the last four in Tokyo three years ago and steered the Dallas Mavericks to the National Basketball Association finals this season, became a big-name absentee from the Olympic basketball tournament, which tips off on July 27.
"Congrats to Greece. They played better than us," said Doncic.
"They have an amazing team. Very well coached. They have Giannis, it's a lot. But also other players. Very experienced team. They know how to play basketball."
Doncic was his team's top scorer with 21 points but Slovenia always trailed after the Greeks raced away to lead 32-14 by the end of the first quarter.
The comfortable lead meant Antetokounmpo played only 21 minutes, scoring 13 points. Thomas Walkup led Greece with 19 points.
Greece, which has not taken part in the Olympic Games since 2008, must beat either Croatia or the Dominican Republic in the tournament final on Sunday to qualify for Paris.
The event in Piraeus is one of four tournaments this weekend to determine the last four places in Paris. The others are in Riga, Valencia and San Juan, Puerto Rico.
Hosts France, defending champions the United States, Canada, Australia, South Sudan, Japan, Serbia and Germany have already qualified.
