Two Rikers Island guards were quickly fired yesterday after pleading guilty to running a “Fight Club”-style disciplinary system that led to the 2008 fatal beating of 18-year-old inmate Christopher Robinson — but, by copping pleas, they avoided longer prison sentences.

Michael McKie is to get two years on Jan. 17, but he’s been in jail 21 months, so he’ll have just weeks left.

Khalid Nelson is to get one year.