I managed to do it a few times with only 8 skill res too, but you need enough HP restore and some avg res(avg res is more important for boss, if you don't have that much bring Greater Healing Potions for Yamachon OR pull him with the mobs around him to absorb and restore HP).
I have like ~30% HP restore and 25% absorb atm. I use Fireboots and 100 helm so I'm working with 35 block, also 26 avg res and 23% skill res. The grudge has 44% avg.
The TL;DR is: HP restore is king and follow Keno's tips.