Neil Lennon's men fell behind after 28 minutes in Transylvania, where they came up against a physical Cluj side that proved dangerous on the break.

But Celtic recovered quickly after falling behind and Forrest's composure in front of goal helped to earn them a result that puts them in control ahead of the return fixture on Scottish soil on August 13.

The Bhoys face a trip to Motherwell in domestic action before then and Lennon will be glad to have emerged from this game with a positive result, although he will have to check on the fitness of Jozo Simunovic after he left the field with an injury.

Odsonne Edouard drove a raking shot towards goal after four minutes that Cluj goalkeeper Giedrius Arlauskis got down well to save.

Celtic was just about on top after 26 minutes when Cluj burst forward with a sweeping counter-attack and Mario Rondon slid the ball between Scott Bain's legs and into the net.

The visitor did not lose its composure, instead piecing together a neat passing move after 37 minutes that culminated in Forrest drilling a low shot in off the post.

Bain made a superb one-handed save to keep Celtic on terms when Billel Omrani struck a close-range shot early in a second half that became increasingly scrappy as Cluj grew frustrated.

Mateo Susic was fortunate to escape with only a yellow card after a scything retaliatory challenge on Scott Brown, and Celtic slowed the pace of the game down in the closing stages with Simunovic's apparent injury the only disappointment on a satisfactory night for Lennon's side.