Kris Commons gave the Scottish champions a sixth-minute lead before Gordon took over and continually denied the Zagreb attack with a world-class showing.
After the win, which saw Celtic stay second on the group table, Deila spoke highly of Gordon who so far has been a brilliant replacement for the imperious Fraser Forster who left for Southampton in the summer.
"Craig was unbelievable. I said to him in the dressing room that we have him to thank for conceding zero goals and winning the game," Deila said.
"Celtic have had good goalkeepers in the past and that is important. It is an important place to have good players.
"He was a prospect to come in before I was the manager of the club but I knew he was a fantastic goalkeeper, who was out for a long time (with injury).
"The goalkeeping coach (Stevie Woods) said he was ready to come back again and he has been an unbelievable signing.
"He can't do much better than he has shown. He can work on his kicking but he is a fantastic keeper and very calm."
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