Former England manager Steve McClaren guided his Wolfsburg team into the Bundesliga top six on Sunday as little Mainz refused to get carried away by their record-chasing start.
Wolfsburg, who lost all three of their opening matches, saw off Freiburg 2-1 for a third consecutive win with Brazilian striker Grafite scoring both goals.
Grafite, the Bundesliga's top marksman last season, opened the scoring in the 25th minute before Freiburg levelled through Senegalese international striker Papiss Cisse, who hit his sixth goal of the campaign nine minutes later. Grafite made sure of the three points with the winner in the 64th minute.
On Saturday, leaders Mainz stunned Bayern Munich 2-1 at the German giants' Allianz Arena to preserve their perfect record of six wins in six games. The result handed Louis van Gaal's struggling side a second league defeat and left them in ninth place, 10 points behind Mainz, who lead Borussia Dortmund by two.
"It was a pathetic performance," fumed Bayern sporting director Christian Nerlinger, after a defeat that means the Bavarian giants have made their worst start to a season since 1977-78. "Mainz were extraordinary, but our situation is precarious. The alarm bells are ringing."
Coach Louis van Gaal added: "A lot of our players performed well below their usual level. I believe Mainz can go far this season and why not think about the title?"
Mainz were in front after 15 minutes when 20-year-old Lewis Holtby swept past Daniel Van Buyten to cross for Sami Allagui. The Tunisian international then beat German international full-back Philipp Lahm before scoring past goalkeeper Jorg Butt with a cheeky backheel.
Bayern, looking a shadow of the team that reached the Champions League final last season, and without the services of Franck Ribery for a month, settled as the half progressed and Miroslav Klose came close with a header in the 43rd minute.
They drew level on the stroke of half-time when Mainz's Danish defender Bo Svensson headed past his own goalkeeper. But Mainz grabbed the winner thanks to another Bayern defensive error in the 77th minute when Adam Szalai drove the ball home.
"We didn't play well. It was all due to Mainz, we just didn't create enough chances," said van Gaal.
Mainz coach Thomas Tuchel, just 37, was delighted by his team's performance. "It's really extraordinary to extend our winning run on Bayern's own ground," said Tuchel. "The confidence that we have built up made the difference."
Mainz are closing in on the Bundesliga record for the best start to a season. Victory over Hoffenheim next week will equal the record of seven straight wins set by Kaiserslautern in 2001-2002 and Bayern Munich in 1995-96.
Dortmund are second in the table with 15 points after defeating St. Pauli 3-1, with Kevin Grosskreutz scoring twice.
Schalke, runners-up last season, had celebrated their first win of this campaign in mid-week with a 2-1 win over Freiburg, but they were facing defeat when they trailed 2-1 at home to Borussia Moenchengladbach. But former Real Madrid star Raul scored his first goal for Schalke when he netted with three minutes left to grab a point in a 2-2 draw.
The draw was enough for Felix Magath's side to move off the bottom of the table with Stuttgart, defeated 4-1 at home by Bayer Leverkusen, taking their place.