The Magpies claimed a 2-0 win at the Etihad to knock out the holders and book their place in the fifth round.
"It's an amazing result," he told Sky Sports News. "I have been here a long time but this is the first win in Manchester.
"The confidence has always been there we just kept working hard and we had a good philosophy, so it's amazing for the whole club, the fans and the manager."
Newcastle will face Tottenham Hotspur in the next round of the Cup.