Apply Texture Atlas to Model Material

I have a model with multiple objects, materials and textures. I want to optimize the textures by creating a texture atlas. As a test, I took four of the textures and arranged them in an atlas image in 4 quadrants. The atlas image is 2k x 2k. Each of the original textures is 1k x 1k.

In each of the existing materials, I replaced the original textures with the texture atlas. I left the tiling for x and y set to 1. But I set the offsets for x and y to the following.

Material for upper left quad: 0, 0 Material for upper right quad: 0.5, 0 Material for lower left quad: 0, 0.5 Material for lower right quad: 0.5, 0.5

But when I run the application, I don't see what I expect. So what am I missing? How do I apply a texture atlas to existing materials?