forms - Is it ok to change the (US) address input field order in favor of a pre-fill feature?

I am working on an international site that requires the user to enter his postal address. I am wondering if it makes sense to have a slightly different order of input fields in favor of a time saving pre-fill feature.

This is the common format for US address input fields:

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A slightly different order might improve the input form UX:

Let's assume it would be possible to detect the City and State correctly after the user entered the ZIP code (I am aware of some ZIP codes not being unique in the US). Once the user left the ZIP code input field (onblur), city and state could be almost instantly be pre-filled.

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My question is:
Would it really harm the user experience if I changed the input field order, i.e. would many users stumble or even drop off?

Answer

I'd rather stick with the well know format since users tend to go to "auto-pilot" in this mode, so making them think isn't recommended. It has also happened to me before that I'm typing / choosing faster then the values are auto-update, creating confusion and sometimes input of double values.

Moreover, you've mentioned it's an international site, so that means:

1. The user has to choose the country first


2. You need to have the reverse lookup service for most countries for this to make sense (and I'm not sure you can rely on that)

Lastly - is the zip code a must? If not, it's better to leave all optional fields to the end.