The result put the German side above Napoli on their head-to-head record and they now know that a win against Marseille would put them into the second round.
"We knew this would be a spectacular game but I didn't expect so many chances and so much excitement," he told UEFA.com. "We wasted a lot of opportunities, but Pepe Reina also made some great saves. We worked hard today and recorded a richly deserved win. However, Napoli were very tough opponents and it wasn't easy for us.
"It was obvious that the team lost their assurance when Napoli pulled it back to 2-1. They didn't realise that the goal actually had no effect on our situation. However, they started to attack again. It was an enjoyable game to watch, but in an intense kind of way."
Arsenal top the group with 12 points ahead of Dortmund and Napoli, who are both on nine.