Alaves won via goals from Carlos Vicente and Carlos Martin, with Dodi Lukebakio scoring late for the visitors.
Pimienta later said: "Alavés behaved as they always do. They are a team that wins duels and second plays, it is something we had warned about. We knew about their potential. We were clear that, in terms of play, we could perhaps hurt them, but if we did not equalise in winning duels and second plays, they would be above.
"And that is what happened. In the first half, in that sense, they outplayed us. All the duels and second plays were for them. They scored a goal, perhaps we could have done more because it was a very quick throw-in. They even had another goal disallowed.
"At half-time, the score was too small for either team's merits. In the second half, we were better, we came close to equalising in the play before the 2-0. Then, with Dodi's goal, we were in the opponent's box for the last ten minutes, with a chance of equalising. If you don't match the intensity of a team, whoever it is, you're in a very difficult position."