Step 1: Distraction
Itachi has a few diversionary techniques up one of them being either a
a Bunshin Daibakuha
(explosive clone) or a Karusu Bunshin
one of his initial Genjutsu could make this distraction.
Step 2: Supression
By only using partial one handed susanoo he can perform this
feat conserving chakra and putting less strain on his body.
This step may not even be necessary if the initial genjutsu is successful.
Step 3: L0L Genjutsu
After forcing eye contact the finishing genjustu (Tsukuyomi)
will leave raikage in a crippled state. K.O