The Ruhr valley club, who last won the Bundesliga title under then coach Jurgen Klopp in 2012, underlined their title ambitions by blowing away their opponents during an explosive four-goal first half performance.
“We showed a really good game today, we started well and instantly took control. The lads enjoyed themselves out there,” Dortmund coach Edin Terzic told a news conference.
“We took a step in the right direction today especially in terms of efficiency. Everyone performed really well and did not ease off at any moment, from keeper to striker.”
The Bundesliga resumes on Friday, March 31, after a break for international matches.
“We are happy to go into the break for international matches with this result. We are overall satisfied with our game and our rhythm,” Terzic added.
Ivory Coast striker Haller, back to full fitness after undergoing cancer treatment earlier in the season, thundered in after a quick passing move two minutes later.
With Cologne playing catch-up it was only a matter of time until Dortmund scored again and Reus superbly rifled in just after half an hour before Malen also got on the scoresheet with a powerful shot that keeper Marvin Schwaebe could not keep out.
Cologne briefly came up for air in the 42nd when Davie Selke cut the deficit with his first goal for the club but despite a slower pace after the break Dortmund still struck twice in two minutes.
Haller tucked in his second goal after a Mo Dahoud free kick bounced off the bar and Reus made it 150 Bundesliga goals and a total of 161 goals in all competitions for the club in the 70th.