A hat-trick from Robert Lewandowski, along with efforts from James Rodriguez, Thomas Muller and Franck Ribery, capped off a memorable win for the Bundesliga leaders at the Allianz Arena.
Hummels, along with the rest of Bayern's defence, was hardly troubled by Dortmund's tame attack, with Mario Gotze's effort against the woodwork the closest Dortmund came to a consolation, and the Germany international felt for his former team-mates.
"There were a lot of ex-colleagues on the pitch today, so of course you feel a bit too," Hummels said.
"I have also lost here [with Dortmund]. I know how much it hurts. But next time it can look quite different again.
"In the second half we played it loose, because Dortmund were limited to trying to limit the score. That was understandable from both sides."
It did not affect Bayern's display, however, as the hosts raced into a three-goal lead by the 23rd minute - Lewandowski and Ribery making it 5-0 on the stroke of half-time, before the Poland forward sealed his hat-trick.
And the veteran head coach was delighted with his side's emphatic victory.
"After an international break, it's often difficult to get into the rhythm. We did that very well.
"The team was very focused from the start. We had to put an exclamation mark and made it outstanding for 90 minutes. Especially in the first half."