Vidak held just an 1,800-vote lead, or only about a 1 percent advantage, over the incumbent Democratic representative with all precincts reporting after Election Day. Tens of thousands of provisional and absentee ballots had yet to be counted, however.
Since the election, late-arriving mail-in ballots were tallied in Kern, Fresno and Kings counties. Costa slowly chipped away at Vidak's lead, and, by Wednesday, Costa had pulled ahead by 1,200 votes. The Associated Press cites the Secretary of State's office as putting the difference at 1,318 votes.
Despite thousands of votes still remaining to be counted, and less than a 2 percent lead, Costa declared victory Wednesday.
"This has been a hard-fought campaign. It appears that it is now over," Costa said in a news release. "I believe our 1,200-vote margin will not only stand up but will increase as the remaining few ballots are counted."
Costa also had a message for his challenger.
"More than ever, we need a less political and more bi-partisan approach; a team effort with all of us in the Valley - Democrats and Republicans - pulling together for a common goal. Andy, I hope you will be part of that bi-partisan team. I will certainly make every effort to reach across the political aisle - as I always have," Costa said.
Costa, who is from Fresno, holds big leads in Kern and Fresno counties. Vidak, who is from the Kings County town of Hanford, more than doubled Costa's vote total there.