Celtic conceded four goals in 21 calamitous minutes on their return to Seville as they let slip a two-goal lead against Real Betis and succumbed 4-3 in a remarkable Europa League match.
Ange Postecoglou’s side lost two goals in quick succession either side of halftime to dent their recent fine form.
The visitors deservedly led through Albian Ajeti’s goal and a penalty from Josip Juranovic, with Socceroo Tom Rogic enjoying a fine game, but their opening group game turned in dramatic fashion just after the half-hour mark.
Juan Miranda pulled one back before Juanmi hit a double either side of a Borja Iglesias goal.
Anthony Ralston headed home with four minutes left but Celtic could not fashion a clear chance to equalise.
Celtic were also without away support with hundreds of fans locked outside Estadio Benito Villamarin following a decree by local authorities in the city which hosted tens of thousands of Hoops supporters for the 2003 UEFA Cup final.
Rogic, a favourite of the former Socceroos boss Postecoglou, tried to spearhead a Celtic revival after they’d gone 4-2 down but Ajeti was denied by an offside flag as he headed home the Australian’s cross.
Midfielder Rogic also volleyed against the post but after Ralston headed home from close range, there was no happy ending for Celtic.
Elsewhere, West Ham earned a comfortable 2-0 win at Dinamo Zagreb after Michail Antonio intercepted a backpass for the opening goal and Declan Rice scored in his 150th game for the club.
It was Rice’s European debut for West Ham, who last played in the 2016-17 Europa League.
Galatasaray beat Lazio 1-0 with a bizarre goal when the Italian side’s defender Manuel Lazzari’s attempted clearance shot straight up into the air and goalkeeper Thomas Strakosha fumbled it into his own net as he tried to catch.
Tottenham put the new Europa Conference League, UEFA’s new third-tier tournament, in the spotlight as they could only draw 2-2 with Rennes.
Spurs were second-best for much of the game after taking an early lead when Lucas Moura’s deflected shot was credited as an own goal by Loic Bade.
Rennes hit back with a goal from Flavien Tait and took the lead when Gaetan Laborde scored in the 72nd minute, but Tottenham levelled soon after through Pierre-Emile Hojbjerg.
Victor Osimhen completed a late double to salvage a 2-2 draw for Napoli against Leicester City, who finished the game with 10 men.
City’s Ayoze Perez got the opening goal at the King Power Stadium and Harvey Barnes looked to have wrapped the match up for Leicester in the 64th minute, but Osimhen got them back in the game with a beautiful lob over Kasper Schmeichel.
He then headed home a dramatic equaliser in the 87th minute, with Wilfred Ndidi shown a second yellow card in stoppage time to add to their disappointment.
Police and stewards needed to intervene following the final whistle after trouble between Napoli and Leicester fans with both sets of fans throwing missiles.
Jose Mourinho’s Roma thrashed CSKA Sofia 5-1 at the Stadio Olimpico with England’s Tammy Abrahams among the scorers, while Steven Gerrard’s Rangers went down 2-0 to Lyon.
Socceroo Milos Degenek’s Red Star defeated Braga 2-1, Monaco edged out Sturm Graz 1-0 while Mesut Ozil scored in his first competitive match in Germany since an angry exit from the national team three years ago as Fenerbahce drew 1-1 at Eintracht Frankfurt.