The Welsh opera singer and her dancing partner scored 26 out of 30 for her jive performance, with judges Carrie Ann Inaba and Bruno Tonioli awarding her nine and head judge Len Goodman giving her eight.
Commenting on their dance, Len said: ''I loved the start, the whole end section - the middle section wasn't really my cup of tea. It was wild and wacky.''
Bruno claimed he loved it for its ''sexiness''.
He said: ''The blonde bombshell is unleashed. I know sexy when I see it and you've got it.''
Roshon Fegan and Chelsie Hightower matched Katherine with 26 points, while Maria Menounos and Derek Hough came second in the leader board for their 'Bonnie And Clyde'-inspired jive which gained her 25 points.
It is the second time Katherine has topped the leader board in the first two weeks, with Carrie Ann saying last week she had the ''best first dance on the first episode ever''.