He killed that ninjabeech without any of that mandatory assistance from a partner like Riggs needed against Jet Li.
Like Riggs needed against the South Africans.
Like Riggs would have needed if he countinued sparring that basic, rookie boxer who owned him.
And its clear from whats happening in the movie at that point, that McClane wanted to take her out in the quickest time possible, as she was forcing the kid to do her evil deeds on the computer that would have screwed up the country more.