Great Britain finished second in Group C at the FIBA U20 European Championship Division B after an 82-61 defeat to hosts Greece in in Chaklida on Wednesday.
Andreas Kapoulas' side secured their place in the quarter-finals with a group game to spare by beating the Netherlands on Tuesday, their fourth success in a row.
But the hosts, and heavy favourites, took control of this one early on before fending off a British fight-back in the third quarter behind the 25-point performance of Vasileios Charalampopoulos.
Jules Dang Akodo had 12 points and six assists for Great Britain while Deane Williams and Callum Lawson contributed 10 points apiece.
The result means GB will face Group D winners Croatia in the last eight on Friday.
The hosts got off to a quick start in front of a packed home crowd, a 13-0 first-quarter run giving them control.
GB turned up the defensive pressure in the second quarter but Greece showed why many of this squad contributed to gold medal success at U18 level 12 months ago, continuing to convert tough, contested shots.
Kapoulas' side responded after the break as Kyle Carey scored the first seven points of the period and the hosts were outscored 22-16 in the third as a whole.
But Greece demonstrated their championship pedigree by finding another gear in the final stanza.