Ok, let me break it down for you;
A 'knight' is armed with a 1 handed sword, a shield, and lance, is mounted on an armoured warhorse and wears heavy plate mail.
A 'samurai' is armed with a daisho, a composite bow, and a smaller tanto, and is mounted on an armoured warhorse (perhaps armed with a spear or other polearm), and wears lamellar armour (which is quite lighter than plate).
A knight often has no true formal training, and learns to fight only in tournament arenas or training grounds.
A samurai learns multiple martial arts, precursors to modern judo, and several other arts (including iaido, iato, kendo, kenjutsu).
Knights win by clubbing their opponents to death or using the brute force of the lance to defeat them with blunt force.
Samurai will engage opponents from a distance with their bow, and in close combat will attempt to defeat their opponent with a perfect attack to a vital point, relying on finesse. Failing that, they will immobilise their opponent and draw their tanto to finish them off.
A knight would find it hard to keep up with the skill and speed of a samurai, but the samurai's weapons are ill-equipped to defeat plate mail, katanas are not supposed to be used to even block an attack, let alone pierce heavy plate mail.
So, neither of the classes has ever faced an opponent similar to each other, and are ill-equipped to fight each other, the knight's lance and heavy sword are near useless, and the shield is merely false security. The samurai's daisho would be unable to find a strike zone on the knight's plate, and would be unable to pierce it, their bows are not made to pierce such heavy armour, their polearm may be able to pierce, but their main advantage is their martial arts skill and tanto, which would be able to find a strike zone and be able to deliver a fatal blow.
tl;dr: Neither are made to fight each other, samurai's skill and versatility would be their best advantage, the knight has no real way to win.
Oh, and later samurai were armed with guns, making it a straight up gg for the knights.