Lars Friis' side lost 2-0 to an OGC Nice Reserve team on Tuesday 2 April on the south coast of France. The first-half remained goalless as Rico Henry returned to the side after a spell out with injury.
The hosts scored two goals in the second 45 minutes to secure a hard-fought victory in the Mediterranean sunshine.
The first chance of the game came when Ali Coote struck a low shot on target after a set by Henry. The captain could only find the gloves of goalkeeper Mouez Hassen, parrying the ball wide. Hassen was a part of Tunisia's 2018 World Cup squad, and showed his experience here with a fine save.
Nice could have had an opening of their own when Pedro Brazao clipped a ball over the top from the left. Patrik Gunnarsson was quickly out to stop a potential one-on-one and took control of the ball.
Coote might have scored at the start of the second period. A lazy pass from Andy Pelmard fell to the midfielder right in front of goal. His shot was blocked on the line by a combination of Hassen and a desperate tackle from Pelmard.
Nice took the lead with a quick counter attack. A ball inside the right channel meant an easy cross for Amadou Ba-Sy to sweep home in the centre. That was after 67 minutes.
Sub Henrik Johansson went close when he charged down goalkeeper Mathieu Pastorelli's clearance close to the goal. It just didn't fall the right side of the post and Nice got a lucky goal-kick.
The home side scored a second on 80 minutes. This time it was a Brentford mistake that helped them on their way. First Fredrik Hammar lost the ball in the middle, then Jonny Mitchell missed his touch completely when it rolled into the path of Alexandre Gameiro. The pacey attacker swept up the field, then placed the ball beyond Gunnarsson.
Brentford B: Gunnarsson; Trialist, Mitchell, Edobor (sub Johansson 81); Dasilva, Oksanen, Hammar, Henry (sub Titov 58); Zamburek (sub Finnsson 58), Coote (sub Majka 74), Hardy (sub Mogensen 58)
Subs (not used): Andersson, Onen, Brissett
OGC Nice Res: Hassen; Mze Ali, Assoumani, Pelmard, Hamache; Brazao, Valtriani, Drame, Sylvestre, Jaziri; Diaby
OGC Nice Res (second half): Pastorelli; Cox, Cisse, Maurin, Lasme; Gameiro, Mestrallet, Trialist, Trinker, Pelican; Ba-Sy