Zabuza can provide a deadly and close match up for a Part 1 Kakashi, with Part 1 Kakashi winning 55% of the time.
A current Kakashi will beat Zabuza nearly 75% of the time. And no holding back? If Kubikiribōchō is coming into range of splitting our favorite Jounin sensei apart. . A kamui will render the dangerous parts of the blade useless and in a different realm.
Kakashi wins this low diff.