Lisboa e Benfica blew a big early lead to lose 80-64 at Tartu Basket, but still made it through from Group C thanks to Lugano Basket's earlier defeat to Lukoil Academic.
Benfica had started the day in need of a win to be sure of going through, and looked to be in determined mood early on as they took a big lead, Ben Reed's three-pointer at the end of the first period putting them up 31-17.
But Tartu scored the first seven points of the second period, and continued to chip away at the lead, getting it down to four, 38-34, on George Tsintsadze's lay-up just before half-time.
But a scrappy start to the second half meant that had to wait until there was only a minute left to go in the third period before they eventually pulled level, 51-51, on Janar Talts' jump-shot.
It sparked a 10-0 run as Benfica, having been caught, began to capitulate.
Tartu finished the game on a 19-5 run to claim only their second win of the group stage.
However, Benfica's blushes were spared thanks to a 90-81 win for Lukoil Academic over Lugano.
Callistus Eziukwu scored 13 points to lead Tartu, while Tsintsadze had 12, Asko Paade, Talts and Silver Leppik all added 12, and Rain Veideman chipped in with 10.
Heshimu Evans had 15 points to lead Benfica, while Sergio Ramos scored 11 and Reed 10.
Lisboa e Benfica Head Coach Henrique Vieira:
"We played well in the first 20 minutes and then relaxed. At the same time Tartu Rock pressed hard and they managed to take the lead and win the game. We are satisfied with the result, our goal was to win all home games and try to make some abroad. So in the next round the goal remains the same."
Lisboa e Benfica player Ben Reed:
"We did not practice for two days and had a hard travel experience, so we started well but then lost the initiative and could not get it back. We made the next round and will try our best."
Tartu University/Rock Head Coach Indrek Visnapuu:
"Congratulations to Benfica for achievement into next round in tournament. Our plan was to play fast and press opponents as much as possible. In first quarter we did not manage but later especially in 3-d and 4-th quarter we played good defence and it made easier to have success in offensive side."
Tartu University/Rock player Georgi Tsintsadze:
"Congratulations to Benfica for reaching the next round. It was a tough and relaxed game at the same time. We started bad, but took the initiative and finally deserved the win. This win does not help us to qualify into next round but gives us emotional charge for upcoming games in Baltic and Estonian leagues"