According to Gabriele Weishäupl, the head of Munich's tourism office, around 6.4 million people will have frequented Oktoberfest by the time the tents close tonight. The total number needs to be adjusted downward a little, however, since the festival's most prominent group of beer guzzlers had their traditional outing cancelled in the aftermath of another confidence-crushing defeat. For the first time in living memory, the players, bits-on-the-side and big-shots of the mighty FC Bayern – the standard-bearers for "we are we" Bavarianism – won't be able to don their Krachledernen. No wonder the tremendously miffed president Uli Hoeness spoke of a "Super-GAU". The term was coined in the wake of the Chernobyl disaster and stands for something that exceeds the "maximum credible accident".

"Take off their Lederhosen" is the chant that's been doing the rounds in the Bundesliga ever since the club from the Säbener Strasse started winning things with annoying regularity in the 1970s. But the enforced exposure of their backsides – and subsequent loss of status and identity – is becoming an everyday scenario this season. A resurgent, young and hard-battling Dortmund side were the latest opponents to register a win against the champions on Sunday night, when Lucas Barrios and Nuri Sahin scored inside 15 minutes after the break. After losing yet another game that was supposed to constitute a turning point, Bayern are languishing in 12th, with eight points from 21. Five goals from seven matches makes them the least prolific attack in the top flight. It's the worst start in their Bundesliga history, a veritable nightmare. "It's high time everybody woke up," said Hoeness.

Louis van Gaal had surprised a few people with a couple of well-intentioned but ultimately futile changes. Edson "not-so-fast Eddie" Braafheid returned at left-back. Bastian Schweinsteiger was moved further up the pitch with Danijel Pranjic playing in his place. Even miss-and-miss striker Mario Gómez was given another chance to find his feet. The 25-year-old looked reasonably sharp in the opening period, when Bayern's pressing made the tired home team suffer. Then, a familiar pattern emerged. "We dominate and create four, five chances and we don't score," said Van Gaal. "Dortmund don't have any chances but the first shot on goal goes in," Jürgen Klopp concurred. "In the first half, we had a lot of problems, we are happy it was 0-0 at half-time," said the Borussia manager. "Bayern were good and could have taken the lead. But they didn't. So we did it instead."

The way to Barrios' deflected opener had ironically been paved by the Dutch manager's one involuntarily switch in personnel. Daniel van Buyten, an Einbauschrank on wheels in recent weeks, suffered concussion and was replaced by the decidedly undivine pony-tail Martin Demichelis, who promptly committed two costly mistakes, a misplaced header and a hand ball, in the run-up to Borussia's goals. And that was that. Bayern capitulated in the face of the black-yellow wave of euphoria in the Signal Iduna Park.

The Bavarians were in full crisis-management mode after the final whistle. Sporting director Christian Nerlinger thought that Bayern needed to lose more than their Lederhosen and shiver their way to victory: "It's time we took away the warm blanket of neighbourly love [in this club]."

"We need to stop deceiving ourselves," said Hoeness. Captain Mark van Bommel showed how much he has internalised the club's philosophy by claiming that the luck of success was mainly due to a lack of effort. "We all need to give 100% and run ourselves ragged on the pitch," he said. "We need to fight." Every Bayern defeat over the past three decades has been explained away in this fashion but, to the Dutchman's credit, he did criticise the club's inexplicable failure to buy a useful defender in the summer too. "I really wanted [Ajax right-back] Gregory van der Wiel to come," Van Bommel revealed the day before the Dortmund set-back. It wasn't the board's fault for a change. Van Gaal had stubbornly refused to spend money and insisted that the existing squad was good enough. The 18-year-old David Alaba, he optimistically claimed, made buying Sami Khedira unnecessary. The young Austrian is out injured though and even Bayern's stubborn manager has admitted second thoughts.

The return of Arjen Robben and Franck Ribéry in coming months will surely turn Bayern's fortunes around after the winter break; an early exit from the Champions League could even see them defend the title after all. But a 13-point deficit behind the sensational leaders Mainz 05 – and a 10-point-gap to Dortmund, whom they take a lot more seriously as contenders – does suggest that it may well be another one of those post-tournament, lack-of-reinforcements campaigns that open up the league to a huge number of contenders. That's exactly how Stuttgart (in 2006-07) and Wolfsburg (2008-09) triumphed recently.

Talking points

• We don't know if Jürgen Klopp had another €50 bet on Mainz 05 partying to victory against Hoffenheim on Saturday, but we do know that Mainz's seventh win in a row has moved the overall odds in Dortmund's favour. The two previous times such perfect starts to the season were achieved, in 1995-96 (Bayern) and 2001-2002 (Kaiserslautern), Borussia ended up hoisting the Schale.

• Mainz won't care too much about this stat, however. "Everything works out for them," lamented Hoffe defender Christian Eichner. Immediately after the 4-2 over TSG 1899, the 37-year-old Mainz manager, Thomas Tuchel, could no longer resist the calls from the stands. He climbed the stadium fence and sang into a megaphone, together with the supporters, Kloppo-style. In the posh seats, the Germany manager, Joachim Löw, called the atmosphere in the Bruchweg Stadion "championship-like" and declared Lewis Holtby's fine pass before the opener [Sami Allagui] "worth the entrance fee on its own". Löw presumably didn't pay for his ticket but the sentiment was true enough: Holtby provided flashes of inspiration that ultimately made the difference against the rather good visitors. The son of an English service man from Stevenage grimaced uncomfortably a little later live on television, when Tuchel exclaimed all his virtues ("always happy to learn, never loses focus, great social competence") in the manner of a teacher praising his favourite pupil. Striker André Schürrle was also outstanding again. Both were surprisingly omitted from Löw's squad for this week's qualifiers but will certainly feature in the friendly against Sweden in November.

• "Some players must have been away with their national teams already," was Felix Magath's take on the 2-1 defeat of Schalke in Nürnberg. The optimism generated by the midweek win over Benfica in the Champions League has evaporated again; 04 are 17th in the table and miles away from playing any decent football. The "defence", in particular, can soon rival Pisa's leaning tower in terms of failed planning and outright wonkiness, and the Royal Blues' efforts weren't helped by a silly red card for Jermaine Jones. To make things worse, keeper Manel Neuer has hinted at his departure in the summer. "I don't feel comfortable with the situation at the moment and have not decided about my future yet," said the 24-year-old.

• Cut and paste Schalke's horrid results, change a few names, take away Magath's Mephistolean landing strip on his forehead – and you have Christian Gross frowning in the face of another defeat for Stuttgart. The Swabians are getting further and further sucked into the relegation quagmire and seem to have acquired the proverbial lack of fortune struggling teams are accustomed to. They thought a late strike from Cacau had rescued a point against Frankfurt, but referee Felix Brych had seen an offence that no one else had. "The football gods are against us," said Gross.

Results: Hannover 0-1 St Pauli, Hamburg 2-1 Kaiserslautern, Mainz 4-2 Hoffenheim, Nürnberg 2-1 Schalke, Gladbach 1-1 Wolfsburg, Freiburg 3-2 Köln, Dortmund 2-0 Bayern , Stuttgart 1-2 Frankfurt, Leverkusen 2-2 Bremen.

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