Jeff Dial, on his third attempt to get elected, finished slightly ahead of fellow Republican Bob Robson.
The pair beat out Rep. Rae Waters, the Democratic incumbent. She trailed Robson by about 1,400 votes with all 59 precincts counted in the Nov. 2 election.
There was an open seat in the district that takes in parts of Chandler, Tempe and Ahwatukee due to Rep. John McComish seeking, and winning, a Senate seat in the district.
The race has been marked by high independent expenditures.
Waters was the beneficiary of $30,423 in such spending in October, but Republicans spent $64,279, the most for any legislative candidate in the state, in the same period against her.
Waters, who considers herself a moderate, held the seat Robson gave up in 2008 when he was termed out.