Malen strikes late to hand Dortmund victory over Cologne
Dortmund lacked offensive fluidity throughout the game, carving out few chances in either half as they shook off the summer cobwebs.
With the match heading towards a rare goalless draw, Malen curled the ball in from a corner in front of Dortmund's famous yellow wall, sending the home fans into raptures.
The match was Dortmund's first competitive home fixture since last season's shock 2-2 final day draw against Mainz, which handed the title to Bayern Munich for the 11th straight year.
Dortmund controlled proceedings early but the best chance of the opening half fell to Cologne after 18 minutes.
Striker Davie Selke's shot copped a deflection from Dortmund defender Niklas Suele and kissed the top of the bar before cannoning into the yellow wall.
Home manager Edin Terzic used up all five substitutions as the clock wound down, Cologne going close to scoring one of their own when breaking Dortmund several times on the counter.
With two minutes of regulation time to go, newcomer Felix Nmecha flicked a Julian Brandt corner into the path of Malen, who fell as he curled the ball into the top left corner.
Dortmund withstood a late charge from Cologne to hold on to a valuable three points.
Terzic said his side had "possession, but too much of it was not in dangerous zones."
"We're unsatisfied, the boys are unsatisfied, and that's a good sign. We're happy about the three points."
His counterpart Steffen Baumgart said his team would "go home a little bit sad" but told Sky "other than the result, plenty worked today."
Leverkusen beat Leipzig
Earlier on Saturday, a stunning chip from Florian Wirtz earned Bayer Leverkusen a 3-2 home win over RB Leipzig.
Fresh off a 3-0 thumping of Bayern Munich in the Super Cup, Leipzig were stunned by two quick first-half goals by Jeremie Frimpong and Jonathan Tah, before pulling one back through Dani Olmo.
The 20-year-old Wirtz looped a cutback from Frimpong over Leipzig goalkeeper Janis Blaswich in the second half, restoring Leverkusen's two-goal cushion.
The visitors scored with 20 minutes remaining through newcomer Lois Openda, but failed to find an equaliser as Leverkusen continued to impress under coach Xabi Alonso.
The Spaniard said he was "satisfied" with the performance, "especially the first half" but said his young team "need to keep working on our mentality" after twice letting Leipzig back into the match.
Borussia Moenchengladbach debutant Thomas Cvancara converted a penalty in the seventh minute of injury time to snatch a 4-4 draw in a thriller in Augsburg.
Gladbach led 2-0 after 27 minutes but Augsburg fought back to level the scores at 3-3 by half-time.
Ruben Vargas looked to have helped Augsburg to a comeback victory when he scored with 14 minutes remaining, but Cvancara's second goal of the match snatched Gladbach a point.
Freiburg started the season with a 2-1 win at Hoffenheim.
The visitors took the lead late in the first half after a Hoffenheim own goal before Roland Sallai doubled the advantage in first-half injury time.
Former Liverpool defender Ozan Kabak pulled one back in the second half.
Elsewhere, Wolfsburg gave promoted Heidenheim a rude welcome on their top division debut, winning 2-0 thanks to a first-half Jonas Wind brace.
Stuttgart overcame this week's loss of captain Wataru Endo to Liverpool with a 5-0 home win over Bochum.
The home side, who saved themselves from relegation with a two-legged playoff win over Hamburg last season, won thanks to doubles from Silas Katompa Mvumpa and Serhou Guirassy and a Dan-Axel Zagadou goal.