Olivier Giroud struck the only goal of the night.
Sarri remarked afterwards: "I think we didn't play very well, I didn't like the first half because we moved the ball only horizontally and slowly, so it was hard to be dangerous. It was better in the first 20 minutes of the second half but we didn't manage the last 15 minutes well. The best thing about this evening was the result.
"It wasn't easy to play a good game here, it was all the conditions to play badly, but I think we could have done better."
Chelsea are now into the next round and Sarri added: "I think the first target in this competition was to qualify and now the second target is to win our group so I think we need one more point. It's very important because then we can talk again about this competition in February, when we will have another target."