Bayern Munich in league slump, admits Guardiola
Dortmund's Henrikh Mkhitaryan (L) and Bayern Munich's Philipp Lahm during their Bundesliga match in Munich on April 12, 2014 - by Christof Stache
The reigning European champions have failed to win any of their three league matches since wrapping up the German title last month with a record seven games to spare and were humbled by Dortmund in the top of the table clash.
Goals by Borussia's Henrikh Mkhitaryan, Marco Reus and Jonas Hofmann condemned 10-man Bayern to their first home league defeat since October 2012.
"In the first half we didn't get going and in the second half we dropped off our game somewhat," said Guardiola, who won 14 titles in four years as Barcelona coach.
"That's a problem you have when we've already won the league. It already happened to me at Barcelona.
"Until now we've been a very good team defensively. Today we didn't show that," added the Spaniard, who has already won three titles in his first ten months at Bayern including the UEFA Super Cup, league and Club World Cup.
They are also in contention in the Champions League where they are defending champions and face Real Madrid in the semi-finals later this month.
This was Bayern's second successive league defeat after crashing 1-0 at mid-table Augsburg last Saturday and being held 3-3 at home to Hoffenheim.
The defeat allowed second-placed Dortmund to trim Bayern's lead at the top of the table to 17 points from 25 just three weeks ago.
Munich's director of sport Matthias Sammer was more critical, especially as Bayern finished with ten men after defender Rafinha was sent off in the dying stages for striking Mkhitaryan in the face.
"We had problems with our rhythm and our build-up play," he said.
"We didn't concentrate enough... We never made the right decisions."
"As a result you can't develop any pressure. We weren't concentrated enough at the decisive stages... but our players aren't robots and have feelings too.
"We're German champions, but we have to be careful and get back to playing well."
Although Guardiola named a full-strength side, it was Bayern's heaviest defeat in any competition since being routed 5-2 in the 2012 German Cup final by Dortmund at Berlin's Olympic Stadium.
- 'We were cheeky' -
The Bundesliga giants are on course to meet again in this season's final on May 17 with Dortmund hosting VfL Wolfsburg in Tuesday's semis, 24 hours before Bayern entertain second-division Kaiserslautern in the other tie.
"We attacked them early, that is the only way to survive here," said Dortmund goal-scorer Reus.
"If you turn your back here briefly, it gets very difficult, that was the secret to our success."
Having beaten Real Madrid 2-0 on Tuesday as they bowed out of the Champions League with a 3-2 aggregate defeat in the quarter-finals, Dortmund claimed their second major scalp in four days.
"We were very cheeky, very consistent and we could have done things a bit better here and there, but when you beat Bayern 3-0, then everything is pretty perfect," said Dortmund coach Jurgen Klopp.
"That was another highly concentrated performance."
This was Dortmund's second win of the season over Bayern after they beat the Bavarian giants 4-2 in the German Super Cup in July before Munich romped to a 3-0 Bundesliga win at the Westfalenstadion in November.