The Democratic challenger, Ms Maria Cantwell, took the edge over a veteran Republican incumbent, Senator Slade Gorton, as the final votes were tallied in the unsettled seat of Washington in the US Senate contest.
With all but one of the state's 39 counties reporting, Ms Cantwell had a lead over the three-term Seattle senator, Mr Gorton, of almost 2,000 votes. The tight margin means the race will be subjected to an automatic recount, starting on Monday.
"Our long journey has come to a spectacular conclusion," a Cantwell spokesman, Mr Ellis Conklin, said. "We're going to win. They can't catch us now."
Mr Gorton's office was subdued. Senator Gorton would not concede but described himself as "cautiously pessimistic" - awaiting the recount.
After more than 2.4 million votes were cast in 39 counties, the race was close. Ms Cantwell had 1,199,260 votes, or 48.7 per cent, to 1,197,307, or 48.6 per cent, for Mr Gorton - a difference of just 1,953 votes. A Cantwell victory will give the state two female senators for the first time in its history and will also tie the Senate 50-50 in the first even split in a century.
Republicans would not lose their advantage for long, however.
If Mr Al Gore wins the White House and the vice presidential candidate, Senator Joe Lieberman of Connecticut, turns over his seat to a Republican appointee, Republican membership would rise to 51 seats.
But if Mr George Bush wins the presidency, his vice president, Mr Dick Cheney, would be able to break ties in a 50-50 Senate.