Pica is a fairly powerful fighter who is hard to pin down since he can merge into the rocks to escape. As long as there is any Earth around him, he will be tough to stop. That said, Zoro is still a lot stronger here and can slice through just about anything. That means Pica will have no true hiding spots and ultimately he will fall to Zoro’s immense power. Pica just isn’t fast enough to have any alternate path to victory. Zoro wins.