Ben Woodside scored a game-high 17 points and hit a go-ahead lay-up late in the contest as BCM Gravelines Dunkerque won 67-64 at Sport Lisboa e Benfica.
Averaging team highs in points (16) and assists (5.1) before Tuesday's game in Portugal, the point guard put in another solid display as the French team improved to 2-0 in the EuroChallenge Last 16.
Mouhamed Saer Sene had a great game for Gravelines, scoring 15 points and corralling 13 rebounds while France international Bokolo was also terrific with 11 points, six helpers and nine boards.
Benfica, who got 16 points and 10 rebounds from Elvis Evora, dropped to 0-2.
The hosts were thrashed last week by 35 points at BK Ventspils but came from behind at the weekend to beat Madeira in the Portuguese league.
They had gone in front of Gravelines by nine points late in the first half but didn't press home the advantage.
Instead, Gravelines battled back and made sure it was close until the end.
A drive and lay-up by Jeffrey Greer knotted the game at 62-62 with 2:45 to go and then Bokolo, who had set up Greer's bucket, provided the assist to Woodside as he went in and scored to make it 64-62.
Benfica had several chances to tie it but missed each time and they eventually fouled Woodside, who made two free-throws for a 66-62 advantage.
Woodside would end up nine of 10 at the line on the night.
Ben Reed's lay-up brought the Portuguese back to within two points and fouled on the play, he had a chance to get them even closer.
But Reed missed the free-throw.
Nevertheless, the hosts played good defense on Gravelines' next possession and didn't allow them to beat the 24-second shot-clock, so with 14 ticks remaining Benfica went in search of a potential game-tying, or game-winning basket.
Dounia Issa had other ideas.
The Gravelines power forward stole the ball from Reed and passed to Greer, who was fouled.
Greer made just one free-throw with six seconds to go to give Benfica one last chance to pull level but captain Sergio Ramos, coming out of a timeout, was off target from behind the arc.
Christian Monschau (Gravelines coach):
"Benfica were very solid in defense and offense. Mike Williams, who has been my former player and whom I know very well, was very useful to them. We improved after halftime. We corrected some aspects in our defense and that was crucial to win the game today. The qualification to next round is wide open. Any of the four teams can go through."
Jeffrey Greer (Gravelines player):
"We've changed our approach to the game in the break and we started the 3rd period better. Our defense improved after halftime and we won the game because of it. Benfica's offensive game was good in the first half and we had to stop them wisely. Our qualification group is very balanced and all the teams are very similar. It will be a very tight competition."
Henrique Vieira (Benfica coach):
"We played a good game but we took some bad decisions in the last minutes. It could happen to anyone and this night happened to us. We had no luck in our last actions in the game. We missed a key player for this game, but my team performed well. We were outstanding in defense, they scored just 67 points tonight. We missed Heshimu tonight. He gives extra boost to the team in defense and offence because of his physical contribution to our game."
Elvis Évora (Benfica player):
"We almost did it. We were so close to win the game tonight. We had a good game but we lost more defensive rebounds than usual, and that means giving some points to the other team that could be crucial when playing a very tight game like the one tonight. We will play every game to win. We want to qualify to the next stage."