Jessica and Nick: Nick Responds to Divorce Petition

TMZ has obtained Nick Lachey's response to the divorce petition of estranged wife Jessica Simpson, and the groundwork is now laid for a fight over money.

In his response, Lachey claims the date of separation was December 13, 2005. In Simpson's papers, she claims the date of separation was November 23, 2005.

Since the couple did not have a prenup, income earned before the split is community property -- divided 50/50.

TMZ has learned that on December 5, 2005, Simpson received $850,000 for performing at a private concert in Cincinnati. If Lachey's separation date is accurate, he'd be entitled to half her fee. If Simpson's date is accurate, she'd keep the entire amount, as well as any other income she earned after November 2.

Source: TMZ