Mohamed Salah struck for the 1-0 win in Spain on the night.
Slot said afterwards: "I almost feel really sorry for Girona, they are such a high quality team and they deserve much more than three points that they have so far. They had a really good game plan today but we had a really good goalkeeper!
"I would have loved to have seen Darwin score because he needs a goal and that's why I kept him on the pitch for quite a long time. He was a threat but when a striker doesn't score you're always asking yourself whether it's a not good play or because of lacking confidence.
"Girona lost a lot of quality in the summer so to play like they do and give us, Feyenoord and PSV so much difficulty says a huge amount about them."
On Alisson's comeback game, he added: "Alisson definitely didn't look like he'd been out for two months. I joked with the players that maybe they wanted to see how ready he was because they let him make so many saves. But he showed why I always say that he's our number one."
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