Dortmund bounced back in style from their 3-1 Champions League defeat to Olympiakos with a dazzling performance reminiscent of their championship-winning form of last season.
It was their fourth successive league win, putting them on 19 points from 10 games.
Poland international Lewandowski, who has seven goals in 10 games, scored either side of half-time after goals from Shinji Kagawa and Marcel Schmelzer had given the hosts an early cushion.
Captain Sebastian Kehl powered in a header on 66 minutes to complete the rout.
"We showed how important goals are in a game," Dortmund coach Jurgen Klopp told reporters. "Our outstanding pressing game and passing game made us better than our opponents. It was very difficult to defend against what we offered today."
Borussia Monchengladbach dropped to fifth on 17 points after Hoffenheim forward Vedad Ibisevic, starting for the first time after a months-long injury break, struck on 56 minutes to give the hosts a 1-0 win.
VfB Stuttgart's Mexico international Maza rescued a 2-2 draw at Nuremberg with a header at the far post six minutes from time. The draw was enough to move them into third on 17.
Hamburg SV, with new coach Thorsten Fink in charge, came from a goal down to earn a 1-1 draw against VfL Wolfsburg, with Mladen Petric cancelling out Mario Mandzukic's first-minute goal with a lovely chip over keeper Diego Benaglio.
The draw lifted Hamburg, still looking for their first home win in more than seven months, off the bottom into 17th place.
It was one-way traffic in Dortmund from the start, with Japan international Kagawa scoring from close range after good work from Kevin Grosskreutz down the left on seven minutes.
Germany international Schmelzer doubled the lead with the first Bundesliga goal of his career, a curled shot from 14 metres after Cologne defenders allowed Mario Gotze too much space in the box. Lewandowski added another in the 44th.
With Cologne, who had won three of their last four games, still dazed, Dortmund's Neven Subotic rattled the crossbar on the stroke of half-time.
The hosts struck twice more in the second half, with the disappointing visitors offering their first and only shot on goal in the 86th minute.
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