How are order executions prioritized?

Hello,

I would like to know how the stock executions are prioritized.

I am aware that its prioritized based on price and time basis however i am not clear on what is the next level of priority for execution?

For Example: What if 2 people place buy orders at the same time and for the same price and stock. Whose order would be executed first in this case?

Specially the After Market Orders would be sent to the markets at a time by all the brokers due to which the time of receiving the orders would be almost the same and the price may be same in most of the orders, whose order would be prioritized in such cases?

Looking forward for a response.

Thanks
Sukesh