Originally Posted by Jonathan Locke

I think the samurai, even though the knight has an extremely well-protected body, that ultimately becomes his downfall. The knight is basically moving slower than the agile samurai, and even more slow if his weapon of choice is a pike. Sure, the samurai would have to get a very precise and well-aimed slash to even gash the knight's flesh, through the armor's thin (but opened) spots (such as between the helm and the neck-cover).
The knight would probably win the battle if it was in a closed space, since he wileds a long weapon (pike or greatsword), while the samurai would obviously win if it was in opened space.

snip.