Senate Democrats notched their first victory of the evening just as the polls closed in Virginia, where former Gov. Mark Warner (D) is the projected winner over his predecessor, former Gov. Jim Gilmore (R).
With only a small fraction of precincts reporting, Warner was carrying 60 percent of the vote, according to state election officials.
Election officials in Kentucky and Georgia were also closed polling places at 7 p.m. Eastern Standard Time on Tuesday, although the key Senate races in those states are too close to call.
With 607 of 3,550 precincts reporting, Minority Leader Mitch McConnell (R-Ky.) was carrying 52 percent of the vote against wealthy businessman Bruce Lunsford (D), according to the Kentucky State Board of Elections.
In Georgia, Sen. Saxby Chambliss (R) was out in front of state Rep. Jim Martin (D) in early returns, 57 percent to 40 percent, according to the Georgia secretary of states office although the race is expected to tighten. Libertarian candidate Allen Buckley was garnering about 3 percent of the vote. If neither Chambliss nor Martin takes more the 50 percent of the vote, the two will square off in a Dec. 2 runoff.
Polls also closed at 7:30 p.m. in North Carolina, where Sen. Elizabeth Dole (R) faces a tough re-election matchup with state Sen. Kay Hagan (D). In early returns, Hagan was beating Dole, 58 percent to 39 percent. About 3 percent of voters chose Libertarian Christopher Cole.
Polls closed at 8 p.m. in New Hampshire, where surveys have shown Sen. John Sununu (R) trailing former Gov. Jeanne Shaheen (D), and in Mississippi, where Rep. Roger Wicker (R) is slightly favored against former Gov. Ronnie Musgrove (D) in a special election.
Election officials in Colorado, Minnesota and New Mexico are set to close the polls an hour later. In the Centennial State, Rep. Mark Udall (D) is facing former Rep. Bob Schaffer (R) in an open-seat Senate race, while Reps. Tom Udall (D) and Steve Pearce (R) are squaring off in the Land of Enchantment Senate contest.
And in what could be the nail-biter of the evening, Sen. Norm Coleman (R) is up against comedian Al Franken (D) in the Gopher State, where polls also close at 9 p.m. EST. Former Sen. Dean Barkley (I) is a major factor in that race.
In Oregon, where Sen. Gordon Smith (R) is being challenged by state Speaker Jeff Merkley (D), polls will close at 11 p.m. Eastern time. And in Alaska, voters have until 1 a.m. to cast their ballots in the race between Sen. Ted Stevens (R) and Anchorage Mayor Mark Begich (D).