Celtic suffered their second successive Europa League defeat this season as they were comprehensively beaten 4-0 by Bayer Leverkusen.
First-half goals from Piero Hincapie and Florian Wirtz put the Bundesliga side in complete control against Ange Postecoglou's side in the Group G clash at Celtic Park.
Lucas Alario added a third from the penalty spot after the break as Gerardo Seoane's side followed up their opening victory over Ferencvaros, while substitute Amine Adli completed the rout with a thumping strike deep into stoppage time.
The result means Celtic were handed an 11th reverse in their last 18 home European matches, while this was the 16th time in 25 outings they have lost to German opposition.
Both sides had chances to break the deadlock during a blistering start to the contest.
Alario was denied by the offside flag inside the opening minute, then moments later a magnificent last-ditch intervention from Jonathan Tah prevented Kyogo Furuhashi from sliding into an empty net at the other end.
Leverkusen had Lukas Hradecky to thank for a couple of important touches in quick succession, the goalkeeper denying Furuhashi and Carl Starfelt.
However, the visitors broke the deadlock in the 25th minute. An untimely slip from David Turnbull allowed Mitchel Bakker to get into the penalty area, where he cut the ball back for Hincapie to turn home.
The lead was doubled following a quick-fire counter 10 minutes later, with Paulinho picking out an unmarked Wirtz to score his sixth goal in as many games for his club.
Hradecky came to Leverkusen's rescue again with saves to thwart Furuhashi and Jota at the start of the second half, but the visitors put the game to bed in the 58th minute.
Alario calmly sent Joe Hart the wrong way from the spot after Cameron Carter-Vickers was deemed to have blocked Paulinho's shot with his arm.
Adli rounded out the scoring in the fourth minute of stoppage time, rifling into the roof of the net after being set up fellow replacement Nadiem Amiri, capping a rapid counter.