User blog comment:12th Supernova/Chapter 778: A King's Resolve, A Pirate's Attack/@comment-75.72.183.14-20150226184847/@comment-24769684-20150226192342

Also, don't forget that Zoro was completely thrashed by Issho before he battled Pica. Even though Zoro completely outclasses Pica, he's still leagues below the best and it was better for his growth as a swordsman to beat Pica like that.