Celtic are still without a point in Europa League Group G as Bayer Leverkusen produced an impressive display to come away with a 4-0 victory at Parkhead on Thursday night.
The German side, who sit second in the Bundesliga, raced into a two-goal lead at the break as Piero Hincapie's opener (25) following a slip by David Turnbull was added to by the exciting teenage prospect Florian Wirtz 10 minutes later as the visitors pounced on another mistake from Anthony Ralston.
Kyogo Furuhashi had seen two presentable opportunities pass him by with the game level as Lukas Hradecky kept out his effort while a piece of last-ditch defending from Jonathan Tah prevented a certain goal inside the opening minutes, but Leverkusen's superiority and class eventually told.
Referee Marco Di Bello awarded them a second-half penalty when he adjudged Cameron Carter-Vickers to have handled from Paulinho's shot with Lucas Alario tucking home the ensuing spot-kick (58) and there was still time for substitute Amine Adli to complete a routine victory with an emphatic finish in stoppage time (90+4).
The result means Celtic already find themselves in a difficult position to reach the Europa League knockout stages after two defeats in Group G, as Postecoglou turns his focus towards a huge Scottish Premiership encounter away to Aberdeen on Sunday, live on Sky Sports.
Celtic: Hart (7), Ralston (7), Starfelt (5), Carter-Vickers (5), McGregor (5), Rogic (6), Turnbull (5), Abada (6), Montgomery (6), Jota (6), Furuhashi (6).
Subs: Giakoumakis (n/a), Bitton (6), Ajeti (n/a), McCarthy (6).
Bayer Leverkusen: Hradecky (9), Frimpong (7), Tah (8), Hincapie (7), Bakker (7), Aranguiz (6), Demirbay (6), Diaby (7), Wirtz (8), Paulinho (7), Alario (7).
Subs: Retsos (n/a), Amiri (6), Schick (6), Adli (7), Bellarabi (7).
Man of the match: Lukas Hradecky.
Celtic's rebuilding work laid bare
Postecoglou's side have now won only two of their last eight games in all competitions, including a 4-3 defeat by Real Betis in their Group G match.
Celtic are in sixth place in the cinch Premiership, six points behind leaders Rangers and return to league duty at Aberdeen on Sunday and will be boosted by aspects of their performance and by having some key players back.
There was a lot of speculation around which of the Celtic players recovering from injury would start the game.
Hoops fans in a packed and noisy Parkhead were delighted to see the return of captain Callum McGregor and striker Furuhashi with Greek striker Giorgos Giakoumakis, yet to make his debut, on the bench.
Celtic team news
Ange Postecoglou made three changes to his Celtic team and there was a huge boost with the return of Kyogo Furuhashi. He joined captain Callum McGregor and Adam Montgomery in the starting XI.
Josip Juranovic, James McCarthy and Albian Ajeti dropped out from the side which drew 1-1 with Dundee United.
Former Celtic right-back Jeremie Frimpong was in the Bundesliga side but striker Patrik Schick, who scored a double - including a wonder goal - for Czech Republic at Hampden Park in their opening Euro 2020 game, was among the substitutes.
The game burst into action. Within a couple of minutes, Leverkusen striker Alario had the ball was in the back of the Celtic net after keeper Joe Hart had spilled a shot from Wirtz, only to be ruled offside.
Seconds later at the other end, Furuhashi sped into the box and rounded keeper Lukas Hradecky and set himself to stroke the ball into the empty goal but was robbed at the last second by defender Jonathan Tah before Hradecky made saves from Furuhashi and defender Carl Starfelt.
Hart had to be smart a close-range effort from Moussa Diaby but he had little chance when the German side took the lead.
Turnbull slipped near the byline which allowed Mitchell Bakker to cut the ball back for Hincapie to sweep the ball in from 16 yards despite the efforts of young left-back Adam Montgomery, also back in the side.
The Celtic defence was in disarray when Paulinho played in Wirtz who knocked the ball past Hart and into the net which left a very different complexion on matters.
Furuhashi tested Hradecky again at the start of the second half with a shot on the turn before the keeper made an even better save from Jota with winger Liel Abada missing the target with the follow-up shot.
A penalty shout when Frimpong knocked over Turnbull was ignored by referee Marco Di Bello but when the former Hoops defender drew a save from Hart with a drive, Paulinho's shot from the rebound was judged to have hit the arm of defender Cameron Carter-Vickers.
Alario sent Hart the wrong way with the spot-kick and the tie was effectively over.
Moments later, Hradecky brilliantly saved a header from Jota and Furuhashi hit the side netting with the rebound and another great chance was missed.
In the 74th minute, amid a glut of substitutions, Giakoumakis replaced Turnbull but it was Hart who had to make the next save, a header from Schick, who had also come on before Adil hammered in a fourth on the break. Now Celtic must regroup and get ready for the Dons.
What the manager said
Celtic boss Ange Postecoglou told BT Sport: "It's disappointing as we had some great chances. It's the story of both boxes but they are a good side. They were clinical inside the box and we were wasteful. We made some mistakes that you can't make at this level.
"So it's disappointing overall. There were a couple of moments where Kyogo may have felt he could've done better but to be fair, their goalkeeper has pulled off some unbelievable saves as well. It's good to have him back in the team as he makes a difference but it wasn't enough tonight.
"I'm disappointed for our fans tonight. They created such a great atmosphere and we had a fine start to the game where we took it to them and created some good opportunities. It's sad to walk away tonight having lost 4-0. We're all very disappointed in the dressing room and we should be. We must have a reaction.
"We've made things difficult for ourselves [to quality]. Even towards the end, there was no need to concede a fourth. It shouldn't have been a 4-0 game. We should've been stronger mentally towards the end to keep ourselves in it. It made things difficult but now there's not to be a reaction.
"We've just got to keep persevering. We've been disrupted by a number of injuries and we've rebuilt the squad. It's not surprising it'll take time, but even within that I know we can be better. We need to use the disappointment to fuel some fire to turn things around."
Analysis: Leverkusen class shines through
Sky Sports' Andy Walker:
"They've lost convincingly. It was a terrific start to the game, played at a really good pace and Celtic created a number of chances before they fell behind.
"There's been some naivety from Celtic tonight in their defending especially, but take nothing away from Leverkusen. Their experience has shone through, although I thought the penalty was harsh on Cameron Carter-Vickers.
"Joe Hart has made a couple of saves tonight to keep the score down but having said that, Celtic are a team that makes chances, but for the Leverkusen goalkeeper. He's made at least three terrific saves.
"An entertaining game but Celtic have lost quite convincingly."
Celtic's defensive vulnerability exposed - Opta stats
- Celtic have conceded 2+ goals in each of their last nine UEFA Europa League games. Since the competition was rebranded in 2009, only Slovan Bratislava have had a longer such run in the competition (11 games between 2011 and 2019).
- None of Bayer Leverkusen's last 21 matches in European competition has been drawn, with the German side winning 13 and losing eight.
- Celtic failed to score for the first time in 20 matches in European competition (incl. qualifiers), since a 2-0 Europa League defeat at CFR Cluj in December 2019.
- German sides have won six of their last seven European away games against Scottish sides (L1), with Leverkusen winning the last two against Rangers and Celtic respectively. Indeed, Celtic have been responsible for four of those defeats, losing to a different club each time.
- With Florian Wirtz (18y 150d) and Piero Hincapié (19y 264d) finding the net, tonight was the first time Bayer Leverkusen have had two teenagers score for them in the same major European game.
Celtic are back in Scottish Premiership action on Sunday when they visit Aberdeen, live on Sky Sports; kick-off 12pm. They will be back in Europa League action on Tuesday 19 October when they host Ferencvaros at 3.30pm.
Bayer Leverkusen face Arminia Bielefeld in the Bundesliga on Sunday, before traveling to Real Betis on Thursday 21 October in the Europa League.