Create a template for the sink by setting it, sink-side down, on top of a piece of cardboard and outlining the edges. Take the sink off the cardboard and draw a line ¾ inch inside of the outlined edge. Cut along the inside line with scissors. From underneath the countertop, find the center of the cabinet and drill a hole into the countertop large enough to put a finishing nail through.
Set the template on top of the counter. Find the center of the template and line it up with the hole in the countertop. Poke a finishing nail through the holes in the template and the countertop. Center the template over the countertop and outline the template onto the countertop. Remove the template and run masking tape along the edge of the outline. Then replace the template and outline of the sink onto the masking tape. Remove the template.
Drill a ¾-inch hole with a dill and spade bit inside the outline closest to the center. Brace the countertop with 2- by 4-inch lumber, to prevent the section that will be cut out from binding.
Cut out the outline closest to the center with a saber saw, using a blade made for cutting countertops. Take the masking tape off the counter. Place the sink into the cutout and trace the edge lightly with a pencil. Remove the sink and run a line of silicone caulk around the cutout, in between the cutout and the traced outline.
Set the sink into the opening and press the edges firmly into the silicone caulk. Level and remove any excess caulk. Attach the faucet and drain and check for leaks. Run a plastic putty knife along the edges of the sink for a finished look.