Celtic are on the brink of Europa League elimination after crumbling to a 4-1 home defeat to Sparta Prague.
Neil Lennon's side have just one point from their opening three group games leaving their hopes of reaching the round of 32 in tatters at the halfway stage. Lukas Julis' hat-trick (26, 45, 76) did most of the damage at an empty Celtic Park.
Substitute Leigh Griffiths reduced the arrears (65), but after Julis completed his treble, Ladislav Krejc compounded the home side's misery with a fourth in the final minute of normal time.
The result leaves Celtic facing a mountain to climb in Group H - bottom on one point - with Sparta leapfrogging them up to third on three points. Lille usurped AC Milan at the summit following a fine 3-0 win at the San Siro.
Celtic: Bain (5), Frimpong (5), Duffy (3), Bitton (4), Laxalt (6), Brown (5), McGregor (5), Christie (5), Rogic (5), Elyounoussi (4), Edouard (5).
Subs: Griffiths (6), Ajeti (n/a), Ntcham (n/a), Elhamed (5).
Sparta Prague: Nita (7), Vindheim (6), Pavelka (7), Plechaty (6), Hancko (7), Sacek (7), Krejci (7), Polidar (7), Karabec (7), Moberg-Karlsson (8), Julis (9).
Subs: Krejci (6), Dockal (6), Lischka (6), Plavsic (n/a), Travnik (6).
Man of the match: Lukas Julis.
Celtic fall short in Europe again
This was Celtic's first meeting with their Czech opponents in European competition, and the hosts were bidding to avoid a third straight Europa League home defeat for the first time. Meanwhile, Sparta's squad headed to Glasgow decimated by health issues and injuries, with first-choice goalkeeper Milan Heca and Slovakian stopper Dominik Holec both out.
Lennon spoke prior to kick-off of the need for his side to "earn the right" to take maximum points from this double-header in their bid to catch up with Group H pace-setters Milan and Lille. But they were second best during a very flat opening half as Sparta deservedly led 2-0 at the break.
Celtic, who reached the round of 32 last season, lacked confidence and desire as Nir Bitton's poor clearance led to David Moberg Karlsson crashing his shot against the woodwork. It was a first shot across the bows of their opponents, but Celtic failed to heed the warning.
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Sparta continued to pour forward with Scott Bain producing a fine one-handed save to tip over Julis' volley into the ground. But from the resulting corner, the Celtic defence was statuesque as the striker was on hand to lash his finish high into the net after Bain had initially tipped David Hancko's header onto the post.
Celtic went with the same starting line-up that beat Aberdeen at Hampden Park last Sunday to secure their place in the Scottish FA Cup Final. Lennon stuck to a 4-2-3-1 formation with Christie, Rogic and Elyounoussi behind Edouard.
The visitors made six changes from the team that lost against AC Milan. Heca, Celustka, Lishcka, Hanousek, Travnik and captain Dockal were all absent. Hancko passed a fitness test, however, and started at left-back while Krejci returned from suspension.
Having failed to register a chance of note, Mohamed Elyounoussi was denied a fifth goal in as many games as he stretched to meet Ryan Christie's cross but his effort grazed the crossbar. Lennon prepared his rousing half-time speech, but his side fell further behind.
Karlsson was the architect as the former Kilmarnock winger did brilliantly to keep the ball alive down the right and after his cross was collected by Adam Karabec, Callum McGregor sold himself too easily for Julis to cut inside and curl his shot beyond Bain.
Left with a mountain to climb, Julis was gifted the chance to complete his hat-trick within a minute of the restart after Bain's sloppy pass presented the ball straight to him, but his left-foot effort was wayward.
Lennon had to show his cards, with a change of shape or personnel, and both Hatem Abd Elhamed and Leigh Griffiths were summoned on the hour-mark - just after Jeremie Frimpong's fierce low shot flashed wide.
But Celtic continued to look devoid of ideas as Michal Sacek drove forward unopposed only to see his shot cannon off the post. A minute later, Celtic had a lifeline as Tom Rogic's cute turn and shot forced Florian Nita to palm the ball straight into the path of Griffiths for a simple finish.
Sparta understandably tired having just played the two other Europa League group stage games since the start of last month with no domestic fixtures, but Celtic were undone once more by their lack of defensive organisation in the absence of Christopher Jullien and Kristoffer Ajer.
Karlsson tormented Shane Duffy on the counter and his low cross was gleefully tapped home by Julis for his third and the 13th goal conceded by Celtic in their last six games.
There was still time for that to become 14 to rub salt into the wounds as Krejci was afforded the freedom of Celtic Park to meet Borek Dockal's cross to head beyond Bain with ease.
Celtic boss Neil Lennon: "It was poor. We started the game OK and then got really ragged with the ball. I keep saying if we don't defend set-pieces properly we'll get punished.
"There was a lack of hunger tonight and I don't know where it's come from because we've put in a really good performance on Sunday. I've defended the players up until now but that was unacceptable tonight.
"There needs to be a culture change within the club. I need to look at the culture, get them more hungry, get them back to basics. All those things Sparta did. We have to be far more aggressive in our play. As the manager I have to accept responsibility but the players have to look at themselves too.
Man of the match - Lukas Julis
Julis had been earmarked as Sparta's chief threat having scored six domestic goals this term, but the 25-year-old arrived on a barren run in European competition.
Then again, he hadn't been faced with Celtic's makeshift defence before, and the 6ft 2in striker tormented Duffy and Bitton throughout.
Julis ended a run of 12 Europa League matches without a goal emphatically, with his last strike coming way back in March 2016 during a last-16 contest against Lazio.
His hat-trick was the first scored away to Celtic in Europe and on another night, he may well have scored more.
- Celtic have lost their last three home UEFA Europa League matches, conceding at least three goals in every defeat.
- After a winless run of five UEFA Europa League games (D1 L4), Sparta Prague registered their first win in the competition since a 1-0 win over Southampton in November 2016.
- Excluding qualifiers, this was only the third time Celtic have shipped four goals in a home European match, also doing so in September 1989 (5-4 win over FK Partizan, Cup Winners' Cup) and September 2017 (0-5 defeat to PSG, Champions League).
Celtic travel to face Motherwell on Sunday, live on Sky Sports Football. Coverage starts at 11am with kick-off at 12pm. Lennon's side return to Europa League action on Thursday November 26 away to Sparta Prague at 5.55pm.