The Belgian playmaker opened the scoring early in the first half, finishing off a fluid move after Emre Can lost the ball in midfield for the visitors.
Dortmund skipper Marco Reus struck the leveller after 84 minutes, but with the clock ticking towards stoppage time, Phil Foden coolly slotted in the winner to provide Pep Guardiola's side with the advantage heading into next week's second leg.
"When they came back to 1-1, it a shame but it happens," De Bruyne said.
"The reaction from us was good.
"2-1 is a tricky score but at least we go ahead with the second leg. In the first half we had a little bit of difficulty creating chances but we did better in the second half. We maybe should have scored more.
"They play really well between the lines and it happens, the reaction was good and we had a good game."
The 29-year-old was just happy that City pounced on the chances and that he could provide for his teammates.
"I can't really remember the beginning of the action but Phil played it across to Riyad and we pounced on the opportunity," he said when recalling the opener. "It was good for us.
"I try to look up before I get the ball, I try to get a picture of what is happening and I was seeing Phil and Gundo running to the second ball so I tried to chip it.
"It was good that it went just above the defender. It was a good action, that's all that matters."