Tom Rogic's Celtic side are in danger of missing out on the Champions League group stage after a 1-1 first-leg draw at home to a 10-man AEK Athens left their third qualifying round tie finely poised.
Comfortable winners over Alashkert and Rosenberg, Celtic found it far tougher against the Greek champions and must now secure an away result if they are to reach the play-off round.
Brendan Rodgers' men had appeared likely to take a lead to Athens when Callum McGregor broke the deadlock inside 20 minutes, only for his opener to be cancelled out by a rasping Viktor Klonaridis strike in the 44th minute.
And it was AEK who finished the far happier of the pair as they absorbed a wealth of second-half pressure following Konstantinos Galanopoulos' dismissal for a second bookable offence with just over half an hour remaining.
McGregor was at the heart of a confident start for Celtic, the midfielder testing Vasilios Barkas with a firmly struck effort from just inside the area.
It was the only warning the Scotland international would offer as, in the 17th minute, he picked out the bottom right corner, firing low across Barkas from the edge of the six-yard box.
But a largely encouraging first 45 minutes came undone on the stroke of half-time, Klonaridis rifling in an unstoppable equaliser.
Marinos Ouzounidis' men bravely protected parity for the remainder of the match, Celtic substitute Leigh Griffiths going closest to a winner with a header after he came on for Australian midfielder Rogic after 63 minutes.
But it was to be one of few real scares for AEK, who defied the numerical disadvantage to hold the upper hand for next week's return leg.