This service (sometimes called “Vesperal Liturgy”) is prescribed only a few times each year.*
It opens with the blessing used at Divine Liturgy: “Blessed is the Kingdom . . .”
The service continues similar to great vespers. There is no psalter reading, and there is an entrance with the gospel book.
After the 3 Old Testament lessons, there is a small litany. The Divine Liturgy then follows, beginning from the Trisagion, followed by the prokeimenon, epistle, etc.
*The days calling for its celebration in some or all years include: Dec. 24, Jan. 5, March 25, Holy and Great Thursday, Holy and Great Saturday. Following the principle “the greater the feast, the shorter the fast,” it is celebrated (a) when there is a pre-festal Divine Liturgy on the eves of certain great feasts, and (b) on certain special days coinciding with the strict fast of Great Lent. In these situations the fast is longest, with the result that the Divine Liturgy comes at the end of the liturgical day. (By contrast, on Pascha, for example, there is no fast at all, so the celebration of the liturgy takes place as soon as possible.)