Just three days before they try to overturn a 1-0 first-leg deficit against the Spanish giants, Bayern fell behind twice against Bremen at the Allianz Arena before scoring four second-half goals without reply.

The flattering scoreline failed to mask Bayern's woeful first-half defending, which must sound the alarm bells for coach Pep Guardiola given the danger of conceding an away goal to Real.

Bayern have conceded the first goal in seven of their nine matches since winning the Bundesliga title late last month with a record seven matches to spare.

Once again the Munich defence was left wanting in the first 45 minutes before the reigning European champions roared back.

Bayern blasted Werder 7-0 in Bremen last December, but they got off to a bad start in the return when Congo midfielder Cedrick Makiadi found Czech defender Theodor Gebre Selassie unmarked and he fired the visitors into a 1-0 lead after 10 minutes.

Bayern were behind for just 10 minutes as veteran striker Claudio Pizarro put in a superb pass which Franck Ribery darted onto and slammed past Bremen goalkeeper Raphael Wolf.

Only a clearance off the line from Bremen captain Clemens Fritz denied Pizarro Bayern's second after a deft chip with half an hour played.

But Bremen grabbed their second when Argentinian striker Franco di Santo found midfielder Aaron Hunt unmarked and the former Germany international slammed home his shot on 36 minutes past despairing Bayern goalkeeper Manuel Neuer.

It could have been 3-1 at the break as Bremen defender Santiago Garcia hit the back of the net from a corner, but the effort was ruled out for offside.

Bayern equalised for the second time when Thomas Mueller headed on Ribery's corner and Pizarro was on hand to stab home his shot to make it 2-2 on 54 minutes.

And they took the lead for the first time three minutes later when Ribery combined with left-back David Alaba and the Austrian international squared for Pizarro to fire home his second.

Germany midfielder Bastian Schweinsteiger then powered home a bullet header from a Philipp Lahm cross to make it 4-2 on 61 minutes before Netherlands winger Arjen Robben hit the top corner of the net to make it 5-2 on 74 minutes, less than 60 seconds after coming off the bench.

Second-placed Borussia Dortmund go to Bayer Leverkusen later, while VfL Wolfsburg squandered the chance to go fourth in the table, and get amongst the Champions League qualifying places, when they were held to a 2-2 draw at home to Freiburg.

Eintracht Braunschweig remain rooted to the bottom of the table after their 2-0 defeat at Hertha Berlin with USA international John Brooks and Tunisia striker Sami Allagui scoring the capital club's second-half goals.

Striker Shinji Okazaki became the highest-scoring Japanese player in a single Bundesliga season when he scored his 14th goal to break Shinji Kagawa's previous record in Mainz's 2-0 win at home to Nuremberg.

Okazaki headed his side's opening goal to break Kagawa's two-year-old mark.

Kagawa, now with Manchester United, scored 13 goals in his final season for Borussia Dortmund in the 2011/12 season before moving to Old Trafford.