The defeat on their own patch means that the newly-promoted outfit are still searching for their first win on their return to La Liga.
"We have played our worst game at the most important moment. We should have offered a little more," he told reporters at a press conference.
"We messed up. But we now need to be united and go forward together. It was much more enjoyable in the summer than it is now, but we have to keep our heads up and move on."
Almeria are currently bottom of La Liga.