BERLIN, Sept 16 (Reuters) - Arminia Bielefeld came from behind to win 2-1 at home to Bayern Munich on Saturday, handing the Bundesliga champions their first defeat of the season.
Mark van Bommel scored six minutes into his league debut to put the Bavarians ahead but a mistake in defence allowed Artur Wichniarek in to equalise in the 25th minute.
Bayern, who won 4-0 at home to Spartak Moscow in the Champions League in midweek, could find none of the same spark in attack and Bielefeld clinched a deserved win when Jonas Kamper blasted in from a free kick six minutes from time.
Werder Bremen, runners up to Bayern last season, were also disappointed. They let slip a 2-0 lead at home to VfB Stuttgart and ended up losing 3-2.
Hamburg SV, who like Werder were beaten in the Champions League in midweek, lost 1-0 away to Borussia Dortmund.
Bayern's defeat meant Nuremberg's 1-1 draw at home to Bochum was enough to take them clear at the top of the table with eight points from four games.
Dortmund's victory took them into a share of second place on seven points, along with Schalke 04, Bayern and Energie Cottbus, who won 2-0 at home to Mainz.
Schalke, who went into the fourth round of matches as co-leaders, will go two points clear at the top if they win away to Hertha Berlin on Sunday.
Bayern were given the perfect start against Bielefeld when Van Bommel, the Dutch international signed to replace Michael Ballack, pounced to turn in a simple chance that came his way at a corner.
The Bavarians looked devoid of ideas on how to increase their lead, however, and slack marking at a free kick let in Wichniarek to head in an equaliser.
Bayern rediscovered some urgency midway through the second half and almost took the lead when Claudio Pizarro headed against the bar from a free kick.
Bastian Schweinsteiger then went on a powerful run through the middle only to be intercepted just as he shot and Pizarro forced a smart save with 15 minutes to go.
Oliver Kahn did well to keep out a shot from Wichniarek a minute later but the goalkeeper could do nothing about Kamper's stunning free kick with six minutes to go.
an happen when you have a Champions League game in midweek,' said Bayern coach Felix Magath. 'We started well but then we were a bit too sure of ourselves.'
Werder looked certain to bring their run of three successive defeats to an end as they took a 2-0 lead against Stuttgart.
Roberto Hilbert back-headed into his own net to give them the lead in the fourth minute and Mohamed Zidan lifted a shot over Timo Hildebrand to double the lead in the 32nd.
Hilbert had the satisfaction of getting a goal back in the 38th, shooting right-footed under the keeper from a Mario Gomez pass.
Stuttgart equalised in the 57th minute through Pavel Pardo and as Werder tired Marco Streller set up Gomez for the winner two minutes from time.