YOU CANNOT BEAT SAM IN THE FIRST ENCOUNTER BY KILLING HIM. YOU CAN ONLY BEAT SAM BY DYING, WHICH IS INEVITABLE.
HE HAS SOME PHASES:
1 THE START ONE YOU CAN'T DO ANYTHING AND THE ARENA IS MEDIUM SIZED
2 THE ARENA IS SMALLER I THINK I DON'T REMEMBER AND IT STARTS WHEN YOU GET AT 50% HP AND AFTER A CUTSCENE. IF YOU TOOK MORE THAN 50% YOU WILL HEAL BACK 2 50%.
3 STARTS AT 0 HP I THINK. ANOTHER CUTSCENE. YOU GET ONE OF YOUR ARMS RIPPED. JUST WAIT. ANOTHER CUTSCENE WILL PLAY AND THEN YOU WILL FINISH THE CHAPTER.

THIS IS VALID FOR ALL DIFFICULTIES.