The poll showed Deal leading by 4 points, which is precisely the poll's margin of error. Isakson, though, is leading Thurmond 47 percent to 35 percent.
InsiderAdvantage conducted the survey Wednesday for WSB-TV in Atlanta with the firm's automated telephone system among 554 registered voters who said they were likely to vote in the November elections. The results were weighted for age, race, gender and political affiliation.
In the governor's race, Deal took 45 percent, Barnes 41 percent and Libertarian John Monds 5 percent; the remaining 9 percent of respondents were undecided. With more than two months until the election, those numbers could change, but if not, Deal and Barnes would wind up in a runoff because neither would have more than 50 percent.
Isakson's commanding lead over Thurmond in the Senate contest could also end in a runoff because of the strong showing of Libertarian Chuck Donovan, who took 7 percent in the poll, while 11 percent were undecided. A more likely scenario is for Isakson's lead to grow when he begins his TV commercials because he also has a large fundraising advantage that would keep Thurmond from airing as many ads.
Libertarian candidates typically poll higher in early surveys than on election day, said InsiderAdvantage CEO Matt Towery.
"Once Isakson begins his television campaign, I expect to see a substantial consolidation of the vote with Isakson likely to move into the mid-50s or above," Towery said. "Michael Thurmond is performing admirably. However, there are relatively few African-Americans with no opinion in the race, and this would, of course, be his most reliable base."
In the governor's race, Towery said, Barnes has remained in contention despite President Obama's low level of support in Georgia and a Republican Governors Association ad tying the two together. At the same time, Deal has held strong without answering the attack ads Barnes has been airing.
"The race really boils down to independent voters," Towery said. "Polling data indicates that virtually as many people identify themselves as independents as they do either of the two dominant political parties. Among independents, the race is tight, with Deal having 41 percent of the independent vote and Barnes receiving 38 percent."