With the score level at 65-65 after four quarters, an additional period was needed to separate Group C rivals Radom and PAOK in Poland.
After the first round of overtime finished 6-6 and the second 8-8, Radom finally secured the win with Damjan Jeszke sinking back-to-back three pointers before Tyrone Brazelton took his tally to 36 to round off the win.
Partizan are 5-0 in the 2016-17 ABA League but needed a lay-up from Stefan Bircevic on the buzzer to overcome MHP RIESEN Ludwigsburg 65-64 in Group E.
The side who sit fourth in the Basketball Bundesliga side had clawed back a 14-point deficit to lead 64-63 in the final minute, but Bircevic stole the win for the Serbians at the last.
Netpunas Klaipeda domestic form may be patchy but the Lithuanian side defeated Muratbey Usak Sportif 67-65 thanks partly to a Larry Drew double-double, while a single point proved the difference as EWE Baskets edged out Ventspils and Openjobmetis Varese beat ASVEL Lyon-Villeurbanne in the other Group C clashes.
Le Mans Sarthe took an early lead in Group B with Ryan Pearson scoring 20 points a 68-49 thumping of Umana Reyer Venezia, with Pinar Karsiyaka in second after a comfortable win over CSM CSU Oradea.
Avtodor Saratov and Maccabi Rand Media also got off to winning starts, dispatching of Khimik and Kataja Basket respectively, while KK Mornar beat Telenet Oostende 74-72.