Harper, the only survivor of Keegan's first spell at the north-east club during the 1990s, told Newcastle's official website: "When we look back we might look at that game and say that was the spark that ignited everything.
"That was the moment the new Kevin Keegan era really began in earnest. I certainly hope so.
"It was absolutely brilliant, fantastic. It was as good a team display as I've ever been involved in.
"It's been a long time coming, but I can't remember a team during my time here playing as well as that away from home.
"It was different class. I think we got a big boost when we arrived at the ground and saw Tottenham had changed their shape to try and match us.
"It meant they were worrying about us and what we can do. It's all credit to the manager for changing the formation a few weeks ago because it has worked."