Nash issued a written statement saying that the couple separated several months ago and were officially going their separate ways, the Arizona Republic said Sunday.
"I am very thankful and excited that we have a new son, Matteo Nash. Alejandra and the baby are doing fine," the statement said. "But this is a bittersweet moment for my wife and me; after five years, we are now in the process of dissolving our marriage."
Matteo was born Friday. The couple's twin girls were born in 2004, one year before they were married.
Nash, who faces the Los Angeles Lakers Sunday, said he wished his estranged wife the best and that he would not be discussing the matter further.