The Chelsea chief executive said: "After the first week I didn't feel Ranieri was up to the job. Having been around a winner like Sir Alex, Ranieri certainly didn't come into that class, so we embarked on looking for a new manager.
"We came up with Mourinho who was young and different.
"We'd seen some of the best names but he was hungry and thought differently and I saw he had some of the same qualities as Alex Ferguson.
"He's a winner and we were lucky enough to get him, and I think we've had some success since then."
Kenyon says Chelsea owner Roman Abramovich's long-term plans for the Blues include Mourinho at the helm.
He said: "There's loads of speculation that if we don't win Jose gets fired, but that's not the way we think.
"It's about winning in style and building that dynasty, and that's what Roman wants to be part of; Chelsea becoming part of Europe's dynasty."