[Jeff Alton]

Any standard length blade in a jigsaw will work. You need to keep firm pressure on the saw so that it does not jump around on you. If you use a fine tooth blade it won't want to jump anyways, it will cut like a hot knife through butter. Drill holes in the four corners of your cut to mark the ends of the cut lines. Drill a hole in the center of the cut out large enough to fit the saw blade in, then slowly move out to the edge. You have lots of control with the jig saw and you can control the speed of the blade easy to help get the feel.

I have done this sort of thing too many times to count with a bunch of different tools and found this to be the most accurate way.

Jeff