Inter were able to grind out a 1-0 Champions League victory on Tuesday.
Sommer said afterwards: "It's really important, against a good opponent. There were some situations in which we had to defend and we did well. We had chances and we are happy with these three points.
"It's important that we defend like this in the Champions League, in games like this it's the details that count. We don't give the opponent many opportunities, that's why we didn't concede goals in all the games. We defended with a lot of balance.
"It is very important to change between the league and the Champions League, focusing on each game. It is important to rotate, we have a good squad and this is a key point for such a long season. Each game can be a step, then we will see."
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