Koscielny partnered Per Mertesacker in the heart of defence and had to cope with a barrage of 17 shots on goal from the home side.
Koscielny told the club's official website: "It was a hard game, Dortmund played very well. We defended well, but to concede a goal two minutes before the end was difficult for us.
"We didn't lose, which was good. We have a game at home, and it is important to win that.
"I think we defended very well - all the team defends together."