The Inter Milan loanee’s strike saw the visitors take a 2-1 victory.
The Inter Milan loanee climbed off the bench to run half the length of the pitch and score to lift Bordeaux up to 11th in Ligue 1 and leave Angers 15th, three points above the relegation zone.
Samuel Kalu’s third goal in four games opened the scoring for the visitors before Mateo Pavlovic levelled in the second half.
Bordeaux took the lead after 31 minutes when Kalu met Maxime Poundje’s hanging cross to stab in from six yards.
Angers levelled after 64 minutes when Bordeaux failed to deal with Flavien Tait’s corner and Pavlovic finished well.
But Karamoh won it in the second minute of injury time when he collected the ball midway inside his own half.
The 20-year-old was allowed to run and he cut inside before firing in low off the post from the edge of the box.