Maxim De Cuyper opened the scoring shortly after half-time before Pascal Struijk received a straight red card following a VAR review for fouling Wilson Isidor.
Despite enjoying possession against the Seagulls, the Black Cats failed to capitalise on their numerical advantage.
Jaouen Hadjam struck in stoppage time to seal Brighton's third consecutive league victory.
“It was a disappointing result,” Le Bris said.
“There were several games within the game - the first half was balanced. It was really tight.
“There was a lot of counter-pressing, and we created a few chances but we lacked quality in the final third.
“At the beginning of the second half we weren’t organised from a long throw and they seized their opportunity.”
“Once the red card came, Brighton wanted to survive. They were compact, they regained possession and they exploited big spaces in counter-attack areas,” he added.
“We have to improve this part of our game. We lacked composure today because our main ideas were good.”
“We must stick to our plan, our principles, trust our teammates, our processes and we must fight.”