How to cut out a rectangle in thick wood?

[OM2]

I am making a box using deck wood.
I want to cut out a rectangle from the middle of one of the planks.

How can I do this?
I have a drill and I have a jigsaw.
The wood is 24mm thick.

I'm sure I could start by drilling a hole...
But I thought I'd ask for advice before trying.

Thanks.

 

[Munroast]

Yes a hole in each diagonal corner, mark the rectangle on the wood and drill just inside the box so as you can't see the drill hole when you have cut it out. If it is important to get a good 90° cut, use a new blade, and choose a section of wood that does not have any knots where you will be cutting, knots can cause jig saw blades to wander a little.