Riku has already defeated Master Xehanort once in battle, in Dream Drop Distance that is. Master Xehanort possessed his younger version after mickey used his stopza spell to freeze everyone and then MX possessed his younger self which caused him to use the keyblade, which he didnt have before (He used his ethereal blades before). Then Riku defeats Young Xehanort possessed by his older self. I think MX should respect the fact that Riku has already beaten him once in battle

That was "young" master Xehanort, and the old master Xehanort has more experience and will surely be more stronger than master Riku. Keep in mind that Terra barely had beaten him in BBS and Xehanort probably was less stronger than how he is right now too.