Celtic suffered a 4-3 Europa League defeat at Real Betis after an impressive opening half an hour had Ange Postecoglu's men two up in Seville.
A tricky first Group G fixture for the Bhoys initially went entirely to plan as Albian Ajeti broke the deadlock and Josip Juranovic's penalty doubled their lead.
But Betis' class told as Juan Miranda and Juanmi netted in quick succession before half-time, a feat the hosts repeated after the break.
Borja Iglesias and a second for Juanmi did the damage for Betis, with Anthony Ralston's late header not enough to ignite an unlikely Celtic fightback as a trip that promised so much ended in disappointment, although their sublime start suggested they could yet have a major part to play in a tough group.
Ajeti, signed by Manuel Pellegrini at West Ham, was influential against his former coach, turning in Jota's cross – the goal awarded after a lengthy VAR review, having initially been ruled out for handball – and then winning a penalty from Claudio Bravo, which Juranovic dispatched.
Joe Hart, who also played for Pellegrini and was replaced by Bravo at Manchester City, made two strong stops between those goals, but he was eventually beaten after 32 minutes.
Moments after a deflected drive struck the post, Miranda burst into the Celtic box to stab past Hart, and the visitors' lead was wiped out completely just 156 seconds later when Joaquin's delicate pass set Iglesias clear to square for Juanmi in front of an open goal.
Betis needed only five minutes of the second half to complete the turnaround, Iglesias meeting Sergio Canales' low left-wing cross with a smart flick.
Again, one goal followed another, with Juanmi controlling on his chest in the area following a corner and firing beyond the rooted Hart.
Tomas Rogic thundered against the foot of the post before Ralston nodded in David Turnbull's free-kick to set up a grandstand finish, but Betis held on.