Nicolas Jackson struck twice, either side of Erling Haaland's equaliser, handing Enzo Maresca his first league defeat as City boss.
Despite dominating possession with 63%, registering seven shots on target and completing 472 passes, the Citizens lacked a clinical edge.
However, Dias praised his teammates' fighting spirit and remains confident of a strong response in their next outing.
“Frustrating, it felt like we fought a lot,” the Portuguese told the media.
“For the first 10-15 minutes of the first half we took our time to get into the game. They changed the way they set up so we took time to adapt.
“But we fought, we had chances and they ended up scoring two goals in two transitions - very efficient. Room to improve, we need to do better.
“I felt like we were dangerous on many occasions, even if the finish wasn’t there we arrived in dangerous places but not able to play. A word of appreciation to the boys because we kept fighting to the end.”