The result left the hosts in 13th place, seven points from safety.
“We were far from our best,” Granero said. “We made many mistakes.”
Huesca moved within five points of safety. “We played more aggressively in the second half,” Etxeita said.
The match at RCDE Stadium ended with Espanyol fans jeering their team, which has won only one of its last eight matches in all competitions.
Barcelona, which holds a seven-point lead over second-place Atletico Madrid, visits fourth-place Sevilla on Saturday. Atletico hosts Villarreal on Sunday, while third-place Real Madrid — nine points off the lead, visits Levante later on Sunday.