I always saved Tidus' overdrives for bosses. I got my Blitz Ace in Macalania, but not the storyline visit, during the Airship visit.

I have the international version, so I went there to fight Dark Shiva. Once I beat her, I decided to train on the chasing guado. I set Tidus' overdrive mode to Victor, kept winning battles and performing overdrives, and I eventually got Blitz Ace!

Rikku tosses the ball for me now because I use her a lot for her Mix overdrive.