Great Britain lost to EuroBasket contenders Greece for the third time this summer, 84-88 in a dramatic finish to their warm-up game at the Copper Box.
GB trailed 84-83 with 24 seconds remaining and stole the ball, but missed a shot and a free throw, with Greece's four free throws sealing the game.
Dan Clark had 23 points to lead GB's scoring, with Gabe Olaseni and Luke Nelson adding 20 and 13 points respectively.
The defeat is GB's fifth in their warm-up games for next month's EuroBasket finals.
On a four-game losing streak after a 72-68 behind-closed-doors loss on Friday to their visitors, GB looked eager to make a mark early, but had to come from behind to share the first quarter 22-22.
Greece were missing four regulars, including NBA star Giannis Antetokounmpo and two other starters, but their wealth of talent - almost the entire squad plays in the continent's top league, the Euroleague - meant they were still tough opponents for head coach Joe Prunty's team.
That showed in the second quarter as centre George Papagiannis, fed by classy point guard Kostas Sloukas, ignited a 10-0 run for a 32-25 lead before Gabe Olaseni and newcomer Luke Nelson brought GB back to lead briefly, 40-39 on Nelson's assured three-pointer.
Down by two points at the break, GB slipped further behind before a storming 14-1 run, inspired by veteran Kieron Achara, brought GB a 65-59 lead at the end of the third quarter.
The return of Sloukas and increased defensive intensity gave the visitors an 11-0 start to the final quarter.
GB set up the chance of an unlikely win with a run of five unanswered point in the last two minutes, but Nelson's drive and shot missed, and when Andrew Lawrence missed a free throw with six seconds remaining, Greece escaped to another win over their hosts.
GB now travel to Warsaw for next weekend's final warm-up tournament before taking the flight to Istanbul for their EuroBasket opener against Belgium on 1 September.
Clark, whose 23 points was his biggest haul in five games this summer, was frustrated with the outcome.
"It's a great test for us to play against a team like that but we should have won today," he told BBC Sport.
"I think we're on the right track, but the biggest thing now is learning how to win.
"It sounds stupid, but there is a process at the end of the game that they do and we don't do, to win games. And we've got to learn how to do that."