Koscielny believes that Thierry Henry's injury-time winner at the Stadium of Light has helped build momentum during a defining week of the season.
"It was very important. We lost three games, then beat Blackburn at home and we came here to win," he told Arsenal Player.
"We played very well. We conceded a strange goal but that's life and we came back and won. That's a good boost for the team and it's better for the games ahead against Milan and Sunderland in the FA Cup.
"Everyone is very happy for Thierry, because he's a good player. The best players can change a game."