Democrat Tim Kaine has won Virginia's open U.S. Senate seat.

Republican George Allen conceded around 10:55 p.m. Tuesday in front of supporters huddled up in Richmond.

The race between Kaine and Allen, two former governors, was one of the nation's most closely watched and most expensive. With the win, Kaine helped guarantee Democratic control of the Senate for another two years.

As of 11 p.m., unofficial returns showed Kaine with 50.7 percent of the state vote to Allen's 49 percent.

Kaine will replace Democratic Sen. Jim Webb, who is retiring.