PHOENIX — Former internet executive Christine Jones’ lead over state Senate President Andy Biggs narrowed Thursday as Maricopa County elections officials began counting the remaining ballots from this week’s primary election.

The battle to replace retiring Republican Rep. Matt Salmon in the 5th District remained too close to call, with Jones now ahead of Biggs by just 578 votes out of the more than 76,000 votes counted for the four candidates in the race.

Jones had led by 875 votes early Thursday before Maricopa County elections officials counted nearly 49,000 ballots Thursday, about 9,800 from the 5th District. They have about 35,000 left to count, with about a quarter of them from the district spanning Gilbert, Queen Creek and parts of Chandler and Mesa. There are also about 3,000 provisional ballots remaining, but many of those are likely invalid.

It’s believed about a quarter of the remaining ballots are from the 5th District.

Jones had 23,083 votes and Biggs 22,505. Former Maricopa County Supervisor Don Stapley and state Rep. Justin Olson remain well behind.

“We are extremely confident that given the returns that we’ve seen thus far, there is a very high likelihood or probability that we have won,” Jones said Thursday. “And we appreciate the support of the voters in this district very much.”

Biggs’ campaign manager, Cesar Ybarra, reiterated his statement from Tuesday night that the margin was too tight to concede. “Today’s numbers just show that we’re continuing to gain ground and it’s still far from over,” Ybarra said.

It will likely take until late Friday or early Saturday to count outstanding ballots that will clear up who won the last uncalled congressional race in the state, said Elizabeth Bartholomew, spokeswoman for the Maricopa County Recorder’s Office.

The district has nearly 190,000 registered Republicans, and the GOP turnout of 35 percent so far greatly exceeds the statewide turnout of 24 percent in Tuesday’s primary election.

The GOP primary winner will almost certainly go on to represent the heavily Republican district.