If you want to know how ZKK happens, it's quite simple:
1st step - Read Oden's flashback fight against Kaido and how he got defeated by being tricked with a hostage.
2nd step - Read Zoro's introduction arc and how Captain Morgan is defeated by Luffy, but gets the finisher from Zoro since Luffy has to take care of Helmepo, who's using Koby as a hostage.
3rd step - Remember that Zoro was also kept in a deal with a scumbag that had no plans on following it through, just like Oden.
I've already said this theory over 3 times in this forum, i'm the only one saying it, so if it happens, i'm an actual prophet of ZKK.