I'm afraid you need to go back a bit further. It seems that Anu was not the first God. In fact, the ancient texts say that Anu's father was Anshar, who was the son of Lahamu and Lahmu. One site that might interest you is: historel.tripod.com/orient/02mesop.htm The "King List" also goes back, if you believe the longevity of the rulers, to more than 400,000 BC. And, the Sumerian Pantheon does not start with Anu.
I wasn't meaning to suggest that Anu was the first God. I was just responding to a post that suggested the fact that belief in him was earlier than belief in Yahweh somehow undercut the Hebrew position.