Callejon struck against his former club with an excellent finish.
The winger said: "I'm happy with my goal and with the victory, but I must say it is probably the most bittersweet strike I've ever scored because it was against a club that's been my home. I know defend another crest to the death. I didn't celebrate the goal out of respect. I wish Espanyol all the best.
"We combined passes from start to finish and scored when we needed to. We were unlucky at scoring in our recent away matches, but we accomplished our mission tonight.
"We all count on this squad and we must defend this crest to the death. Mourinho asks me to play as I know how."