|Pops Mensah-Bonsu had already contributed 27 points to Besiktas when he scored the winning basket, two seconds from time|
Besiktas followed up their historic first Turkish Cup win at the weekend by edging out Nizhny Novgorod 82-80 at the death to keep up their push for first place in Group K of the EuroChallenge.
Perhaps suffering a hangover from Saturday's exertions, Besiktas emerged from the first quarter trailing 26-13 but rallied to force a tense finish, snatching victory thanks to a dunk from Great Britain international Pops Mensah-Bonsu with just two seconds left on the clock.
The dramatic closing stages came thanks to a huge rally from the hosts at the start of the second quarter as they erased their earlier struggles, reeling off a 12-2 run capped by a tip-in from Mensah-Bonsu, to get back in the game, 28-25.
The visitors began to pull clear again but could not regain their early level of dominance as Besiktas stuck with them, and a 6-0 run drew them level, 74-74, on a pair of Mensah-Bonsu free-throws before Carlos Arroyo's lay-up gave them a rare lead with 2:53 to go.
Artem Yakovenko made a lay-up to tie it but Arroyo made it 79-76 with a lay-up and a free-throw with 1:41 remaining.
Semen Antonov's jump-shot cut the gap and after Arroyo missed a jumper, Novgorod were back in front as Antonov sank a pair of free throws.
David Hawkins got to the line for the hosts but could only split his throws, leaving it tied with 12 ticks left, and everything was in the hands of the visitors.
But Yakovenko missed a three-pointer and then committed a crucial turnover, allowing Mensah-Bonsu a dramatic dunk to win it.
Mensah-Bonsu finished with 29 points and 10 rebounds, while Hawkins added 26 points and Ersin Dagli had 11 points and 13 boards for the victors.
Antonov led BC NN with 18 points while Nemanja Protic had 14 and Yakovenko had 12.