eviction after foreclosure, Unlawful Detainer needed or go right to Writ of Possession?

I acquired a house by foreclosure due to due to lack of monthly payments by the previous owner for money I provided as a second loan. I had the previous owner served with a three-day “Notice to Quit” per CCP 1161a(b)(3) (California law). Five days later I began filling in an Unlawful Detainer (UD-100) and noticed at the bottom of the first page “Do not use this form for evictions after sale (Code Civ. Proc. para. 1161a)”.
My question is: what (California) form should I use to proceed with the eviction?