The visitors dominated the opening 45 minutes, creating several opportunities that could have put them comfortably ahead.
However, the Eagles punished their wastefulness, scoring twice before the break and adding another midway through the second half.
Despite the disappointing result, Glasner urged his players to remain positive.
“The oldest rule in football is the goals you don’t score, you concede, and it felt strange being 2-1 down at half-time instead of three or four nil up,” he told media after the match.
“But it was our best performance this season; we created so many chances. They put in a huge effort, but at the end it was always the post or the goalkeeper or missing the target.
“Always when we should have scored, we conceded.
“The most important thing for us is to remain calm, not be negatively influenced by this result, but look at the performance that is improving week by week.”