Brendan Rodgers' first competitive game in charge of Celtic ended in an embarrassing 1-0 defeat to Lincoln Red Imps in the first leg of their Champions League second qualifying round tie at the Victoria Stadium in Gibraltar.
Former Liverpool manager Rodgers was appointed with the hopes of improving Celtic's fortunes in Europe after failing to make the group stage for two successive seasons under former boss Ronny Deila.
However, the Northern Irishman's tenure got off to a disappointing start with part-timer Lee Casciaro – who also works as a police officer – nicking a slender advantage for Lincoln with his second-half strike.
Moussa Dembele was the brightest spark for Celtic in an otherwise dour first-half, having a goal ruled out for what was deemed an illegal challenge on Lincoln goalkeeper Raul Navas.
The 20-year-old forced the keeper into a save low to his right four minutes before half-time, but early in the second half Celtic found themselves behind.
Efe Ambrose failed to deal with a long ball down the middle, with Casciaro latching onto it and turning the centre-back with ease before finding the back of the net with 48 minutes played.
A brilliant run down the right from Antonio Calderon almost resulted in a second for the hosts, but, after cutting inside onto his left foot, the midfielder curled narrowly over.
Dembele's striker partner Leigh Griffiths then saw his shot from Saidy Janko's cutback deflected onto the crossbar by Jean-Carlos Garcia before Roy Chipolina headed over.
Griffiths rattled the bar again with a 20-yard free-kick and, with Erik Sviatchenko's header kept out by Navas with seven minutes remaining, Celtic must wait for next week's second leg to overturn the deficit.