Mr. Tarver received 9,015 votes, or 70 percent of the 13,231 votes cast in the district, apparently drawing a high volume of crossover votes from Republicans in the Hill section, who voted Democratic ballots.
Mr. Williams, who received 3,932 votes, said the crossover vote, which he called a "switcheroo," defeated him.
"The numbers just don't come close to what happened last time," he said. "But it's legal, and the people spoke."
In several precincts where the Republican vote usually runs 65 percent or higher, a higher-than-usual number of Democratic ballots were cast.
For example, in the 2006 primary, Republican House District 119 candidate Barbara Sims received 150 votes at the Woodlawn United Methodist Church precinct, and Mr. Tarver received 90 Democratic votes there in his race for the state Senate. On Tuesday, Mrs. Sims received 129 votes at Woodlawn, and Mr. Tarver received 172 Democrat votes.
Mr. Tarver said he never altered his strategy to win.
"I set a game plan early on, and I'm glad we didn't deviate, even when my opponent made comments about how big he would win," he said.
Had Mr. Tarver lost the election, the political impact in Atlanta would have been negligible, political observers say.
Former state Sen. Don Cheeks said the only difference would be the loss of Mr. Tarver's three years representing Augusta and his cooperation with the majority party.
"However, Ed is a Democrat with a Republican governor and Republican Senate, and he's not going to move up," Mr. Cheeks said. "Maybe (Lt. Gov.) Casey Cagle will give him one of the openings on the Appropriations Committee. The problem is they're never going to give Democrats enough votes on any important committee to have an impact. The majority party will always control the committees. They will keep enough of their own party on any committee to control it."
Ralph Walker, the professor emeritus and director of the research center at Augusta State University, said it takes a term or two for a lawmaker to learn his way around. In reality, it is better for voters to return incumbents to office unless they're doing a bad job, Dr. Walker said.
Mr. Tarver will face Republican challenger John Butler in the November general election, but Mr. Cheeks said Mr. Tarver's win Tuesday means he's won the seat because 59.2 percent of the voters in the district are black.
Dr. Walker, likewise, said Mr. Butler has little chance of winning the seat.
Reach Sylvia Cooper at (706) 823-3228 or firstname.lastname@example.org.