WASHINGTON — Republicans tightened their grip on the Senate early Wednesday, capturing a string of Democratic seats across the South. Democratic leader Tom Daschle struggled for political survival in South Dakota.

Illinois State Sen. Barack Obama, a Democratic political star in the making, easily won a seat formerly in Republican hands in Illinois, and will be the only black among 100 senators when the new Congress convenes in January.

But the GOP did most of the celebrating by far, taking Democratic open seats in Georgia, North Carolina, South Carolina and Louisiana. Rep. David Vitter triumphed there, the first Republican since Reconstruction to win a term in the Senate.

"The nation spoke that we're on the right course, and we'll stay on that course and hopefully accelerate it," said Senate Majority Leader Bill Frist of Tennessee. He said the results showed voter rejection of Democratic "obstructionism" in the Senate. He added that he expects the strengthened GOP majority will be called to confirm one or more Supreme Court nominees.

At nearly 2 a.m. in the East, Republicans were assured of 52 seats, one more than they control in the current Congress.

Three races remained unsettled.

In the one with the most far-reaching national implications, Daschle trailed former Rep. John Thune narrowly with votes counted in more than 85 percent of the precincts.

Sen. Lisa Murkowski, R-Alaska, led in her quest for a full term after winning her seat by appointment from her father, the governor. She led former Gov. Tony Knowles.

In Florida, former HUD Secretary Mel Martinez led Democrat Betty Castor in a late, long count.

The Republican march through Dixie began in Georgia — and spread in several directions at once.

Rep. Johnny Isakson claimed Georgia for the Republicans, and Rep. Jim DeMint took South Carolina. Rep. Richard Burr soon followed suit in North Carolina. Vitter made it four for four when he captured a seat in Louisiana — avoiding a runoff by winning more than 50 percent of the vote.

In each case, Democratic retirements induced ambitious lawmakers to give up safe House seats to risk a run for the Senate.

Republicans also held fast in Oklahoma, where long-term GOP Sen. Don Nickles retired. Former Rep. Tom Coburn prevailed there, despite early campaign stumbles that sent the party to his rescue with a televised attack on his Democratic challenger.

But the GOP string ran out in Colorado, where Democrat Ken Salazar narrowly triumphed over Peter Coors in a race to succeed retiring Republican Ben Nighthorse Campbell.