Johnson City Mayor Phil Roe upset incumbent Rep. David Davis in Tennessee’s 1st District Republican primary Thursday, marking the fourth primary upset of a sitting member of Congress this year.

With 100 percent of precincts reporting late Thursday evening, Roe received 50 percent of the vote to Davis’s 49 percent. Minor candidate Michael Sabri received 1 percent. Just 500 votes separated Roe and Davis as all votes were cast, with Sabri’s 326 total votes the potential difference-maker.

Roe had run a race emphasizing his conservative credentials, winning endorsements from several newspapers in the eastern Tennessee district. Roe also hit Davis throughout the race for taking political donation from a defense contractor accused of bribing Saudi Arabian officials.

“The incumbent failed to key into the anti-Washington fervor that was building out there,” said Jamie Osborne, the Roe campaign’s senior strategist early Friday morning. “We had an outsider message.”

Osborne said the campaign’s anticipation of gas prices as a major issue as early as five months ago was key to crafting Roe’s message and strategy. A poll released in May by Davis’s campaign showed the first-term incumbent leading Roe 61-20.

Osborne added that Davis seemed to have performed the worst in the Tri-City media market, which Davis had saturated with negative campaign ads in the days before the election.

Roe had proven to be a formidable fundraiser opposite Davis in the 2008 cycle and reporting having raised $550,000 to Davis’s $600,000.

Osborne said the campaign “has had discussions” about the prospects of a recount in days close to the election, but noted that when Davis won a multi-candidate primary in 2006, it was only by a margin of 573 votes over his nearest opponent. There was no recount in that race.