What I've done is very different from making the entire battle a mechanical exercise. I know what the overall outcome of the battle will be, for story arc purposes. The party is a vignette in the bigger painting, and while they will presumably prevail in their area, their ability to change the overall course of things was nil.
So I would describe the lead-up to the battle, the approach to the field, and the onslaught/onset. Then I would have a prepared melee for the party. Maybe they were directed to a particular point on the field, maybe they chose a particular group of enemies. But that's the fight they have, and the rest of the world will go on.
When they finish their fight, you can either have a "next fight" if they were too quick, or you can say "as you watch your last enemy drop, you realize the melee is subsiding over the whole of the battlefield..."
It really boils down to your last comment, about the tactical objectives. The party is tactical, within the bigger strategic scope of the world. There are some good examples of this sort of thing in the early Conan books, or in the Jhereg series (Vlad Taltos) by Steven Brust.