Try to have dispel by this point. You can dispel Haste and he won't recast it.
My setup was as follows.
Tidus, Kimahri and Rikku started it off with Tidus casting Hastega to speed everyone up and Rikku casting slow on Evrae. Then I just hacked away with everyone, pulling back when needed and then moving back in. Rikku and Kimahri used Al Bhed potions if needed.
After he cast Haste on himself I brought in Lulu and Auron instead of Rikku and Kimahri. Tidus cast Hastega again so they could be sped up. Lulu cast Dispel removing Evrae's Haste and then Auron and Tidus hacked away while Lulu cast Firaga. Use any overdrives you have now.