This was the second time that Moser, the president of Pennsylvania Republicans for Environmental Protection, had run for commissioner without the party's backing. Aichele and Farrell both received the GOP endorsement.
Joseph "Skip" Brion, the county Republican Party chairman, had remained optimistic that Farrell would pull ahead.
At one point, when Farrell led by only 29 votes, Brion said, "A lot of his base is not in yet. I think we've done very well today."
On the Democratic side, the winners were Bill Scott, 62, a lawyer who served two four-year terms on the West Chester Borough Council, and Kathi Cozzone, 44, an accountant and financial analyst from Uwchlan Township. Scott ran for commissioner in the Democratic primary four years ago, and Cozzone ran for county controller in 2005.
In third and fourth place, respectively, were lawyer Virginia McMichael, 50, an East Whiteland Township supervisor, and Ken Knickerbocker, 51, a software company executive and president of the Parkesburg Borough Council.
Michele Vaughn, who heads the county's Democratic Party, said she was not surprised by the close numbers.
"We knew we had four strong candidates," she said. "The close election is a reflection of that."
The four winners will advance to the general election Nov. 6, and voters will elect three for commissioner.
In other races, Republican David Bortner, a Birmingham Township supervisor and lawyer, will face Democrat Jennifer Levy-Tatum of West Bradford, a lawyer and educator, for a new seat on the Chester County bench.
East Bradford Township auditor Kevin Fitzpatrick, a Democrat, will oppose the GOP's Ryan A. Costello, an East Vincent Township supervisor, for recorder of deeds. Costello won his primary race against challenger David Jenkins yesterday.
Vying for prothonotary will be the incumbent, Republican Bryan D. Walters, and Downingtown lawyer John H. Kiefel, a Democrat. The register of wills ballot will feature Kipp Stone, a Democrat and former bank executive from West Goshen, and the incumbent, Republican Paula Gowen.
District Attorney Joseph W. Carroll and Sheriff Carolyn Bunny Welsh, both Republicans, ran unopposed; however, two Democrats waged write-in campaigns.
Vaughn said she believed Timothy Trott, 52, a lawyer from West Bradford, had secured the necessary 250 votes to appear on the November ballot for district attorney, and Kevin Christie, 53, a former state trooper from Caln Township, would have enough votes to run for sheriff.
Because Chester County has been the last suburban Philadelphia stronghold for Republicans, political analyst G. Terry Madonna has said he believes the commissioners' race will affect politics statewide.
Madonna, the director of the Keystone Poll and a professor at Franklin and Marshall College, said the success of Democrats in recent Chester County elections gave the party momentum going into this year's races. Andrew E. Dinniman beat Aichele for the 19th District state Senate seat last year, and Barbara McIlvaine-Smith won a state House seat in the 156th District in November.
In recent years, GOP candidates in statewide races have regularly lost the once strongly Republican Philadelphia suburbs. Madonna has described Chester County as the "lone holdout."
Republicans still have a voter registration edge in Chester County, but it's no longer the 2-1 advantage they held for decades. The county Board of Elections lists 303,342 registered voters: 156,373 Republicans, 95,153 Democrats.
Contact staff writer Kathleen Brady Shea at 610-701-7625 or email@example.com.
Inquirer staff writer Nancy Petersen contributed to this article.