Jude Bellingham hurled his arms in despair, Bayern Munich’s supporters hooted and hollered in disbelief but, through it all, Thomas Tuchel barely flinched.

What should have been the most challenging opening assignment for the former Chelsea manager – the ultimate showdown in Germany and, almost certainly, a title decider against his old club – turned into the kind of evening that he would have only thought possible in his dreams.

Bayern didn’t just beat Borussia Dortmund, they skewered them to such an extent you wondered how the team in yellow-and-black had arrived in Bavaria as the league leaders; how this hurt Bellingham, who at one point kicked a goal post out of sheer frustration.

Tuchel’s new team were excellent – fast, furious and full of threat – but the helping hand they received from Dortmund or, more specifically, their hapless goalkeeper Gregor Kobel could not be ignored. His calamitous display effectively turned the course of a season for both clubs.

All seemed set for a proper contest in the opening 10 minutes, as thunderous tackles were exchanged; Dortmund even had the opening chance, with Marco Reus having a shot charged down as he charged into Bayern’s area.

Bayern Munich stormed to victory over Dortmund and reinstated a lead at the top of the Bundesliga table on Saturday

But then it all changed. Little seemed to be happening as Bayern moved the ball across their defence to Dayot Upamecano, who looked to set Leroy Sane free with a pass from inside his own half. He had over-hit to such an extent that Kobel came racing out, ready to clear.

Not so. In one of the moments that will be replayed over and over and, almost certainly, will become an internet GIF, Kobel swung a leg to clear, missed it completely and watched in agony as Sane shepherded the ball into a gaping net.

Such was the farce around the goal, even the stadium announcer chortled as he bellowed out Upamecano’s name. Tuchel, however, simply shouted Joshua Kimmich over to give some instructions, refusing to celebrate out of respect to his one-time employers.

As Bayern got the scent of blood, Kobel’s unravelled and, before you knew it, the hosts were out-of-sight thanks to two goals in seven minutes from Thomas Muller, both of which Dortmund’s keeper should have prevented.

Kobel was caught napping as Muller arrived at the back post to turn Matthias De Ligt’s header in then, somehow, he contrived to spill a shot from Sane straight into Muller’s path. When he turned the ball in, Emre Can slammed the floor in frustration and Bellingham roared his fury.

It is no exaggeration to say Bayern could have had five or six before the interval, with Kingsley Coman culpable of an inexplicable miss after rounding Kobel but then losing his footing. The France international made amends early in the second period when picked out by Sane.

Dortmund did, at least, prevent this becoming a humiliation and that was down primarily to Bellingham, who kept showing for the ball and demanding his team-mates do the same. He got some reward in the 72nd minute when winning a penalty after being tripped by Serge Gnabry.

Can, the former Liverpool midfielder, swept in from 12 yards while Donyell Malen poked a shot in on the final whistle but it was too little, too late. The game had long since gone and, perhaps, their best chance of winning the Bundesliga for the first time since 2012 was gone, too. Tuchel, undoubtedly, will certainly hope so.