Serena Williams just welcomed her first child ... a baby girl!!!

The tennis superstar gave birth to a 6-pound, 13-ounce girl ... according to ESPN. Venus Williams moments before her U.S. Open match Friday reportedly told the network, "Obviously I'm super excited. Words can't describe."

Serena had been admitted to St. Mary's Medical Center in Palm Beach, FL on Wednesday and was induced on Thursday.

Serena and Reddit cofounder Alexis Ohanian got engaged last December after dating for about a year. Alexis is also a first-time daddy.

Congrats!!!