The Associated Press called the race Wednesday as Rodriguez clung to a 345-vote lead. Leon, the mayor of Ontario, would have needed to secure more than two-thirds of the roughly 1,000 uncounted votes to stage a come-from-behind victory.
"I look forward to being a voice for all of the people of the Inland Empire, and for safer neighborhoods, at the State Capitol," Rodriguez said in a prepared statement.
The tight margin gave Democrats little breathing room despite party voters commanding a 20-percentage point registration edge in a district that takes in parts of Los Angeles and San Bernardino counties.
Leon switched his party affiliation to "no party preference" from Republican after losing the Senate race to Norma Torres, D-Pacoima.
Rodriguez's win moves Democrats a seat away from reclaiming a veto-proof supermajority in the Assembly after Holly Mitchell of Los Angeles claims her seat in the Senate.
Democrats could pick up another seat on Nov. 19 if Matt Dababneh defeats Republican Susan Shelley to fill the San Fernando Valley seat vacated by Bob Blumenfield.
PHOTO: Voters cast their ballots on Nov. 6, 2012. The Sacramento Bee/Randall Benton