Election results released Monday showed Democrat Josh Newman of Fullerton narrowly defeated Chang, from Diamond Bar.
Newman's victory gives Democrats control of two-thirds of the 40 seats in the Senate. That's enough for them to approve tax increases, suspend legislative rules, pass emergency legislation or overturn the governor's vetoes without any support from Republicans.
Monday's results also showed that Republican Assemblyman Marc Steinorth of Redlands defeated Democrat Abigail Medina in a tight Southern California Assembly seat. Still, Democrats picked up three Assembly seats and will have a supermajority in the lower chamber.