"I think it was very important, more than the Tottenham game," Koscielny told British media. "It was crucial to win here.
"You are always happy because you score a late goal and have three points.
"They had the same points as us and play very direct football. They cross very well and up front they have some players who can score headers, so it was very difficult."
Arsenal have not conceded a goal in the five league games that Shkodran Mustafi, Nacho Monreal and Koscielny have started together in defence.
"It's always important for a defender (to keep clean sheets)," the 32-year-old France international added.
"It's easier for everyone on the pitch when we work together and then afterwards we have the quality to get forward and create opportunities to score. We need to keep this in our heads and continue like this."
Arsenal next host Huddersfield Town in the league on Wednesday.
(Reporting by Hardik Vyas in Bengaluru; Editing by Peter Rutherford)
