What caused the Golden Bowl to go upstream? After finishing the last meal before attaining enlightenment, the Ascetic Gautama threw the golden bowl into the river and said:


  "If I am to succeed in becoming a Buddha today, let this bowl go
  upstream, but if not, let it go downstream." (source)


Gautama was not yet a Buddha and I don't think he had psychic powers to make the bowl go upstream. Even if he had the power, it seems he was not doing it by himself.

Was Gautama expecting some divine being to answer his request? 

Did a Deva or god make the bowl go upstream? If not, how did the Golden Bowl go upstream?
It's called Saccakiriya. It basically uses the power of true speech. But it has to be something strong.

ex:

I have never lied in my life! If that is true, may this happen!

I have never stolen in my life! If that is true, may this happen!

I have never killed in my life! If that is true, may this happen!

Once the Buddha instructed Venerable Angulimala to invoke his Saccakiriya to help a pregnant lady. This is what he said: "Since I was born of Aryan birth, O sister, I am not aware of having intentionally deprived any living being of his life. By this asseveration of Truth may you be well! May thy unborn child be well!" 

In this scenario it's a true statement about the future. There was no Deva involved.