The 21-year-old South Korean forward scored the game's only goal in Leverkusen's victory at Signal-Iduna-Park - as Sami Hyypiä's men stayed within four points of league leaders Bayern Munich.
The result also consolidated Leverkusen's top-two standing, with third-placed Dortmund now six points back through 15 games.
Son's seventh goal of the Bundesliga campaign was a vital one and the South Korea international said he felt a good performance was coming in the build-up to the blockbuster.
"This was possibly our best display so far this season," Son told Bundesliga.com.
"Getting the better of Dortmund is difficult enough and for me to score the decisive goal is, of course, fantastic.
"We've shown many times we can keep up with strong sides and Dortmund, without a doubt, are one of them.
"I had a good feeling going into the game and I'm glad we did so well.
"We should now enjoy our success and then make sure we're again at our best on Tuesday (in the Champions League against Real Sociedad)."
Son's Leverkusen team-mate Stefan Kiessling said his side were not focussed on Bayern's fortunes but just aiming at maximising their points tally.
"The win isn't so much about keeping track with Bayern Munich," Kiessling said.
"We want to play good football and gather as many points as possible. And we're certainly doing very well in that respect at the moment."
