Support for McCain, an Arizona senator, held firm overnight at 29 percent, with former Arkansas Gov. Mike Huckabee sliding one point to 23 percent. Former Tennessee Sen. Fred Thompson climbed two points to move into third place at 14 percent.
A portion of the polling was conducted after former Massachusetts Gov. Mitt Romney's breakthrough win in Michigan on Tuesday, but he still slipped one point to 12 percent. Texas Rep. Ron Paul and former New York Mayor Rudy Giuliani were tied at 5 percent.
"Essentially there was no real movement overnight in what looks like a very stable race," said pollster John Zogby.
"I was looking for a sign of a Romney bounce after Michigan and didn't get it," he said. "He may have to wait another 24 hours before there are signs, but it seems reasonable he would get one.".
The rolling tracking poll of 813 likely voters in South Carolina's Republican primary had a margin of error of 3.4 percentage points.
South Carolina's Republican primary on Saturday is the next battleground as both parties choose candidates for November's election to succeed President George W. Bush. Nevada also holds Republican and Democratic nominating contests on that day.
The seesawing Republican race has produced three winners in the first three significant contests -- Huckabee in Iowa on Jan. 3, McCain in New Hampshire last week and Romney in Michigan.
Romney won Michigan in a campaign that focused on proposals to turn around the state's ailing economy. The economy is also the top issue in South Carolina, the poll found, with 30 percent of voters listing it.
Immigration was next at 17 percent, with the Iraq war dropping to third at 14 percent and the war on terrorism at 11 percent.
McCain leads among a variety of groups, the poll found, including men, women, seniors, independents and Democrats.
Huckabee, hoping to win over the state's large bloc of religious conservatives, led Thompson among those voters who said they were "very" conservative. The ordained Baptist minister also led McCain narrowly among those who said they were "born-again.".
About 10 percent of the poll's respondents said they had not decided on a candidate yet, and nearly half of McCain's supporters said they could still change their minds.
About 45 percent of Romney's backers and 38 percent of Huckabee's supporters also said they could change their minds, leaving plenty of room for momentum swings in the final days.
The rolling tracking poll in South Carolina will continue until Saturday's voting. In a rolling poll, the most recent day's results are added while the oldest day's results are dropped in order to track changing momentum.