An open beaker kept on a table started leaking when two holes were made at the same level. This is because
pressure due to liquid
pressure exerted by the atmosphere
The total pressure is due to the weight of the liquid above the holes and atmospheric pressure acting on the surface of the water. In a liquid, at the same level pressure is equal in all directions. So, when holes were made at the same level, the liquid came out as it was exerting pressure in all directions inside the container.