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This achievement requires some luck, but I got it with the following stats, runes and items:

Stats:
Agi: 7
Str: 50
Vit: 6
luck: 44


Runes:
Assassin
Robustness (doesn't do anything for this achievement)
Vampiric (doesn't do anything for this achievement)


Equipment:
Fallen Lightning (Weapon lvl 10)
Night Shroud (Armor lvl 10)


I didn't had any buff, but if you find luck or strength buffs it might be easier. It may take a few tries to get this achievement because you need a crit on the first hit on the first boss.