The Magpies beat Arsenal 2-0 away from home in the Carabao Cup semi final first leg.
However, Gordon knows that the tie is only halfway done, and that they could easily go out.
He told BBC Radio 5 Live: "Every one to a man was top-level.
"Coming to the place is so hard and they defend really well. It was always going to be a smash-and-grab kind of game for us, but we executed it perfectly.
"We are a team and that's when we play at our best, when everyone's on the same page.
"We have to be that ruthless with and without the ball - all the top teams do it."
On Alexander Isak, he added: "Very good. He is the best in Europe, probably right now, with the form he's in.
"The best quality he's got is that he's so humble.
"He is not scared to pass the ball. He's very unselfish, and his best ability is his raw ability on the ball."
On possibly winning the cup, he finished: "It would mean the world, but we cannot think about that.
"They can easily flip this fixture if we are not at our best levels."