Celtic threw away a two-goal lead to lose 4-3 to Real Betis in a pulsating start to the Europa League group stages, while West Ham cruised to a 2-0 victory over Dinamo Zagreb.
Eighteen years on from reaching the UEFA Cup final in Seville, Celtic returned to Andalusia and got off to a dream start at the Benito Villamarin.
Albian Ajeti bundled home the opener thanks to a VAR review after the goal had initially been ruled out for handball.
The Swiss striker was then chopped down in the box by Claudio Bravo and Josip Juranovic buried his first Celtic goal from the penalty spot.
But the defensive frailties that have characterised Ange Postecoglou’s early days in charge of the Glasgow giants were exposed to cost the visitors a vital victory.