The Chester County GOP secured wins for its two endorsed commissioner candidates Tuesday, but a close vote in one of those races may have Republicans looking over their shoulder.

Commissioner Carol Aichele and her running mate, Recorder of Deeds Terence Farrell, held off a primary challenge by renegade Republican Sandy Moser, an antisprawl activist. Aichele established an early lead and held it, but the returns between Moser and Farrell seesawed for much of the night.

Coming within 1,100 votes of derailing an endorsed candidate adds baggage to the GOP quest to continue controlling the courthouse, a dominance that dates back to the Civil War, according to political analyst G. Terry Madonna, director of the Keystone Poll and a professor at Franklin and Marshall College.

"This is a horrendous environment for the Republicans, and these internal fights don't help," said Madonna, citing discontent in national and state politics. "I think the Republicans clearly understand the Democrats are coming after them full force."

Aichele, 57, of Tredyffrin Township, running for a second term, and Farrell, 59, of Lincoln University, will now face two Democrats for three commissioner seats this fall:

Bill Scott, 62, a lawyer with eight years of experience on the West Chester Borough Council, and Kathi Cozzone, 44, an accountant and financial analyst from Uwchlan Township.

Joseph "Skip" Brion, the county Republican Party chairman, said the results did not surprise him, even though Aichele had struggled to win the party endorsement in February, squeaking by on the third ballot. Farrell easily won party backing on the first ballot.

"I always felt Carol would be the top vote-getter," said Brion, citing her record and name recognition.

Aichele said she was gratified that voters responded well to her accomplishments, and said her numbers showed the strength of the county Republican Party. But she added that she has no intention of being complacent.

"I take nothing for granted," she said.

Both Brion and Aichele downplayed Moser's influence.

"Open space is extremely important, but it has to be done in a fiscally responsible way," said Brion.

Aichele said she and Farrell planned to take "a very strong open-space program" and make it better by adding more municipal and private money to "$15 million in tax-based funding."

Michele Vaughn, who heads the county's Democratic Party - which did not endorse any of its four candidates - believes Moser's showing signals growing dissent within the county GOP, especially on the issue of land preservation.

"This clearly opens the door for two Democrats," she said.

Vaughn said she believed that Scott and Cozzone prevailed because they enjoyed strong support among committee people and had previously run countywide campaigns.

Cozzone agreed.

"I came so close to winning two years ago," she said, referring to her run for county controller. "My numbers were unheard of for a Democrat in a county row office."

Scott, who ran for commissioner four years ago, led the Democratic field, followed by Cozzone, lawyer Virginia McMichael, 50, an East Whiteland supervisor, and Ken Knickerbocker, 51, president of Parkesburg Borough Council.

Madonna said Moser's supporters could prove pivotal to the November outcome, depending on where they throw their support. He pointed out that Republican votes helped Chester County Democrats secure two important wins in seats long held by the GOP. Andrew E. Dinniman beat Aichele for the 19th Senate District seat last spring, and Barbara McIlvaine-Smith won the 156th House District last November.

"The Democrats are making inroads, that's uncontested," said Madonna, calling Chester County the sixth-largest Republican county in the state and the "last to tilt toward the D's."

Brion said he believes that Moser's support base will return to the GOP fold.

"After all, they are Republicans," he said.

Moser, who said her backers included Republicans, Democrats and independents, is not so sure.

"If the party does not make a very strong, convincing commitment to open space, I can't predict what my supporters will do," she said. "Some may stay home and some may support the Democrats."

Contact staff writer Kathleen Brady Shea at 610-701-7625 or kbrady@phillynews.com.