Bricks, Masonry, Asphalt and Concrete - How do you cut into brick to make flush with wall?

My fireplace is the ugliest brick. The opening is a half-circle with the bricks horizontal sticking out at you. The brick goes the width of the fireplace and goes up to the ceiling. I want to drywall over the brick and put up a mantle. I am not thrilled about having a half-circle opening under a rectangle mantle, but not much I can do about that. But I do want to get the brick that juts out to be flush with the rest of the fireplace. How do I do this? Never touched brick before...

Very carefully deeply score the brick all the way around (grinder w/masonry blade, carbide hack saw blade, or a even more carefully with a very sharp cold chisel). Afterward (carefully again) shear the brick with a cold chisel.

If you're considering drywalling up to the firebox opening, re-think that idea. Think tile, thin brick, stone, or something along those lines. Use fire core rock over the chimney.