Celtic’s unbeaten start to the season came to a shuddering halt as they were taught a Champions League lesson by a rampant Borussia Dortmund inspired by the electric Karim Adeyemi.

Daizen Maeda cancelled out Emre Can’s early penalty in a frantic start, but it proved to be the briefest of respites for the Scottish champions.

Adeyemi ran riot with a lethal hat-trick, with another spot-kick from Serhou Guirassy helping the home side to a 5-1 half-time lead.

Guirassy struck again after the break and Felix Nmecha completed the rout with the seventh goal.

The victory sets Dortmund up to take on Real Madrid next in a rerun of last season’s final, while Brendan Rodgers' Celtic will have to improve drastically when they head to Italy to take on Atalanta in two weeks time.

Celtic made the worst possible start, conceding a penalty when Jamie Gittens showed rapid pace to slalom through and lull Kasper Schmeichel into bringing him down in the box. Can coolly converted from the spot.

The response was swift. Arne Engels delivered a beauty of a cross from wide on the right that Maeda bundled in from close range.

If that equaliser was meant to settle down the Scottish champions, they barely had time to draw breath before Dortmund struck again.

The speed of Adeyemi was frightening the life out of the Celtic defence and he raced clear to fire past Schmeichel with the aid of a deflection off Auston Trusty.

The 22-year-old German international produced a moment of magic for Dortmund’s third, firing a rocket high into the net from the edge of the box to make it 3-1.

Celtic players looked unable to catch a breath and things started to really unravel when Engels caught Adeyemi and Guirassy buried the penalty to make it four.

The Yellow Wall was rocking now and Adeyemi had his hat-trick before half-time, firing in another fabulous long-range strike to beat Schmeichel’s despairing dive.

Celtic managed to stop the bleeding for the first 20 minutes of the second half, but Guirassy punished a Alistair Johnson mistake to bury his second and Dortmund’s sixth.

A wretched night was summed up for Celtic when substitute Adam Idah was unable to head into an empty net and Nmecha smashed in Dortmund’s seventh at the other end moments later to bring the curtain down on their humiliation.

After nine wins from nine this season – including an impressive 5-1 destruction of Slovan Bratislava on matchday one – confidence was coursing through this Celtic side before what Rodgers described as an “acid test”.

Celtic have only ever won twice away from home in the Champions League, and never in 14 attempts on German soil. That never looked like ending here.

Drubbings at the hands of Europe’s big guns have become an unfortunate habit for Celtic in recent years, and this mauling will be filed alongside similar thrashings by the likes of the Real and Atletico Madrid, Barcelona and Paris St-Germain.

This Celtic side was supposed to be different, supposed to have found defensive solidity to go with the attacking potency they have displayed this season.

Missing their defensive lynchpin, Cameron Carter-Vickers, it was always going to be a huge task to contain a Dortmund team who looked like scoring every time they flooded forward.

Had it not been for some last-ditch interventions from Liam Scales and good saves from Schmeichel, Celtic's record European defeat of 7-0 could have been beaten.

Sometimes you have to accept the opposition are just levels above, but Rodgers will be frustrated at the unforced errors that compounded Celtic’s problems.

This was always going to be Celtic’s toughest test and they came up desperately short. Now the challenge is to rediscover something much closer to their best for the remaining Champions League games.

Dortmund may have lost some of the key men that helped them to last season’s final, but they look to have all the tools to go deep into this tournament once again.

The likes of Jadon Sancho, Mats Hummels and Niclas Fullkrug may have moved on, but they still have stars all over the pitch and none shone brighter than Adeyemi.

His electric pace, and that of Englishman Gittens, tore Celtic to shreds, with the classy Julian Brandt pulling the strings and picking the holes in the visitors’ ragged defence.

Not many opponents will be as accommodating as Celtic were and tougher tests await, but Dortmund look to have the blend of pace, power and guile to trouble anyone.