American Reyna slammed home like a veteran after being set up by fellow 17-year-old Jude Bellingham as an ever youthful Dortmund began the season with their usual promise.

Erling Haaland, 20, added a penalty and then completed a wonderful team goal.

"It was a seemingly even game, Gladbach did well tactically in the first half," match captain Mats Hummels told Sky after an 11th straight Dortmund win over Gladbach.

"Second half it wasn't that we were so much better. With the quality we have...we can create chances and get goals."

Promoted VfB Stuttgart suffered a disappointing return to the Bundesliga when they lost 3-2 at home to Freiburg.

Fellow newcomers Arminia Bielefeld drew 1-1 at Eintracht Frankfurt while Werder Bremen, who narrowly avoided relegation last season, reverted to type and lost 4-1 at home to Hertha Berlin.

Augsburg won 3-1 at Union Berlin and Hoffenheim beat Cologne 3-2 late on with Andrej Kramaric hitting a hat-trick.

RB Leipzig host Mainz on Sunday with Wolfsburg also taking on Bayer Leverkusen.

Dortmund took the lead when English debutant Bellingham calmly played in Reyna, who finished with aplomb on 35 minutes.

Gladbach had their moments but Dortmund, runners-up last term, went further in front when Haaland stroked home a 53rd-minute penalty after Reyna was tripped.

Dortmund then raced from one end of the pitch to the other with Haaland finishing off a sensational move.

Stuttgart's first game back in the top-flight after a season in the second tier was marred by poor defending, striker Nils Petersen being left completely unmarked to head in Freiburg's opener.

The visitors, who have lost first-teamers Luca Waldschmidt, Robin Koch, Alexander Schwolow and Mike Frantz to transfers, soon grabbed their second through Roland Sallai.

A well-worked move was then finished off by Vincenzo Grifo to make it 3-0 before 2007 champions Stuttgart rallied through Sasa Kalajdzic and Silas Wamangituka.

Ambitious Hertha, who lost to second-tier Eintracht Braunschweig in the German Cup first round last Friday, took the lead in Bremen when Peter Pekarik slid in their first shot on target on 42 minutes.

Dodi Lukebakio soon lashed in Hertha's second just before the break.

A swift attack led to Matheus Cunha sweeping home the third as Bremen's demons returned after a mini-revival saved them late last term. Davie Selke's towering header was a consolation with Jhon Cordoba marking his Hertha debut with a late fourth.

New Hoffenheim coach Sebastian Hoeness had a happy start to his Bundesliga career.

Kramaric scored after four minutes following an error from Jonas Hector.

Cologne levelled through their new signing from Union, Sebastian Andersson, but Kramaric struck from the spot on the stroke of half-time to boost Hoenessi.

Cologne hit back again on 86 minutes through Dominick Drexler but Kramaric had the last laugh in injury-time.

Australian Associated Press