Democratic senator Harry Reid, the most senior Democrat on Capitol Hill, has narrowly held his seat against Tea Party-backed Republican Sharron Angle.
Mr Reid (70) avoided becoming the third Senate party leader since 1952 to lose re-election. He led Ms Angle 51 per cent to 45 per cent of the vote with 41 per cent of precincts reporting.
Ms Angle (61) a former state legislator, had won her party's nomination by defeating the state Republican establishment's choice in a primary.
Ms Angle said Mr Reid and his fellow Democrats in Congress had reneged on their 2008 election promise of change, delivering only high unemployment and mounting government debt.
Nevada's unemployment rate of 14.4 per cent, the nation's highest, plus the highest mortgage foreclosure rate in the United States were fodder for Ms Angle's attacks on Mr Reid and President Barack Obama. Mr Reid was also dogged by voter disapproval ratings that hovered around 50 per cent.
The campaign was marked by sharp partisan and personal attacks in adverts and on the campaign trail over the economy, immigration and what Mr Reid called Ms Angle's "extreme" opposition to government.
Elsewhere, Republican John Kasich ousted Ohio Democratic Governor Ted Strickland, winning in a state that has been hit hard by the recession and will be a major battleground in the 2012 presidential election.
Mr Kasich, a former congressman, had condemned Mr Strickland for his stewardship of the state's economy as governor.
Mr Strickland countered that Mr Kasich was backing policies he said would send US jobs overseas.
Florida Republican Marco Rubio and Kentucky Republican Rand Paul became the first Tea Party-backed candidates to win Senate seats, ensuring an influx of conservative views in the chamber. However, another Tea Party favourite, Republican Christine O'Donnell in Delaware, lost her race.