Inter won 2-1 on Monday to go 15 points clear at the top of the Serie A table.
Sommer told DAZN: "Of course, it was an important victory against a tough opponent and it was the demonstration that we have to fight against everyone because no one gives away points. We are happy for the victory, but not for the performance.
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"It's an effort from the whole team when we don't concede a goal. We're attentive, good at duels, it's easy for a goalkeeper with a defence like this.
"For the goalkeeper it's essential to be focused. When we leave the locker room there's your shirt hanging up and I always stop to look at it."