Borussia Dortmund will be bidding to prove last season was no fluke when it opens its defense of the German league title on Friday by hosting Hamburg in the first Bundesliga game of the season.

With an average age of just over 24-years-old, Dortmund stunned the German league by taking over as leaders after the 10th game of last season and stayed there until the season's end to finish with a seven-point lead.

While Bayern has splashed out in the transfer market to lure the likes of Germany goalkeeper Manuel Neuer and defender Jerome Boateng to Munich this summer, Dortmund has been quietly adding to its young squad.

Talented midfielders Ivan Perisic and Ilkay Gundogan have been added from Club Brugge and Nuremberg for 5 and 4 million euros ($7.11 and $5.69 million) respectively, while defender Chris Loewe has been brought in from third-division Chemnitzer FC.

With exciting Japan winger Shinji Kagawa now back to full fitness after breaking his foot in January, Dortmund coach Jurgen Klopp can call on the bulk of the squad that won last year's title.

Still 19, midfielder Mario Goetze is the rising star of the team, having forced his way into the Germany squad and is earning considerable praise here after a string of eye-catching performances last season.

Klopp kept Dortmund's league rivals guessing last season by using different combinations in attack as the likes of winger Kevin Grosskreutz, midfielder Sven Bender and Paraguay striker Lucas Barrios all made their mark.

However, the one member of Dortmund's title-winning squad to have moved on has left big boots to be filled, with Turkey playmaker Nuri Sahin leaving for Real Madrid.

Klopp, though, will be eager to avoid following the same fate of other recent German champions Wolfsburg, in 2009, and Stuttgart, in 2007, who failed to back up their title success the following season.

Neither team managed to finish higher than sixth the year after their success, something Klopp is determined to improve on.

"We aren't typical champions, we aim to be contenders again," said Klopp, who was voted Germany's manager of the year by Kicker magazine.