Ten-man Celtic threw away an early lead to succumb to a 3-1 defeat to Red Bull Salzburg in Austria.
Record signing Odsonne Edouard gave Celtic the dream start with just two minutes on the clock, slotting home to stun the hosts.
It was backs to the wall for Celtic from there on in, but they could not hold out, with Munas Dabbur and Takumi Minamino turning the match on its head with two goals in six minutes, before Dabbur netted from the spot in the 72d minute to make it three, after James Forrest had hauled down Andreas Ulmer in the box - a foul that earned him a straight red card, with Forrest adjudged to have been the last man.
Celtic's dismal record away from home in the Europa League continues, as they remain without a win on the road in the competition.
The hosts came into this contest on the back of nine wins out of nine in the league - the first time any club has done such in the history of the Austrian top flight - but were caught cold by Celtic with less than two minutes on the clock. Edouard latched onto a long punt upfield, easily shrugged off Salzburg defender Andre Ramalho, before slotting the ball coolly into the bottom corner.
Celtic stood firm until the 55th minute, but the equaliser that came was deserved, with Dabbur steering the ball past Craig Gordon in the Celtic goal, before Minamino poked home from close range to give Salzburg the lead. Ulmer then caught Forrest cold, with the Celtic winger only able to pull Ulmer to the ground in the penalty area, with the red card brandish soon afterwards.
Dabbur stroked the penalty down the middle to make sure of a second group win for Salzburg, who have now gone 49 unbeaten at home in all competitions. Celtic's season, though, is still to really get going.