Raul Jimenez struck the only goal of the game as Harry Wilson took advantage of a Scarles error to find the Mexican with a clever cross.
“We played a good game, we had chances, good chances, and then we got punished in the final moments of the game,” Nuno told West Ham TV.
“The first half was equal, both teams controlling, containing, not too many situations on the boxes. The second half I think we started with momentum, we created a lot of good combinations going forward.
“I saw it in that moment that the goal was coming. Everybody felt it, the fans got behind the team, and the boys, the energy was there. And then in the final moment we got punished.”
On Scarles' error, Nuno continued: “We all make mistakes. It's not about individuals. It's about how can we react as a team when we have an important game in two days.
“We cannot hide from the situation that we are in, but I'm positive that things are going to turn around."