The German midfielder, who came on as a second half substitute, wrapped up a brilliant City display by rounding off a mesmeric 44-pass move for the Blues’ all-important third goal after earlier strikes by David Silva and Sergio Aguero.
And Ilkay said victory in the 177th Manchester derby not only sent City into the international break two points clear at the top – it also helped atone for last April’s 3-2 loss to United at the Etihad.
"It was very important to score the third goal because at 2-1 it is always a dangerous game," said Gundogan.
"The third one killed it because it was so late.
"Unfortunately, we weren't able to score more than two last time but today we scored three and won the game so we're very happy.
"United have ability to create chances and they are dangerous from set pieces. The third one killed it because it was so late.
"When I came on in the second half, he (Pep Guardiola) told me to keep the rhythm high and use the spaces. I played in the middle off David Silva and Fernandinho and looked to use Bernardo and Raheem. We wanted to keep the ball and I think that it worked out well.”
Aguero, sporting a nifty new silver hair style, struck a brilliant second for the Blues straight after the restart, lashing home from a tight angle for his eighth derby goal in 10 starts.
But Kun said he derived more satisfaction from the three points.
"For me it was more important to get three points but it's always nice to score,” said Aguero.
And asked about his new haircut, Kun added "I don't know. Sometimes my hair is crazy!"