According to US media reports, it is expected that after Nevada wins, the Democrats will continue to control the US Senate.
Democratic incumbent Kathryn Cortez Masto looks set to narrowly defeat her Republican rival, former state Attorney General Adam Laxalter.
It came just a day after Democrat Mark Kelly declared victory in Arizona, defeating his Republican challenger Blake Masters, who like Mr Laxalter has the support of Donald Trump.
That means Democrats have 50 seats in the Senate.
Democratic Vice President Kamala Harris can break the 100-member House tie, meaning the party could win for President Joe Biden.
That would be especially important if a seat on the U.S. Supreme Court, which currently holds a 6-3 conservative majority, becomes vacant in the final two years of Mr. Biden’s term.
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The last state to be decided is Georgia, where Democratic Sen. Raphael Warnock faces Republican Sen. Herschel Walker on Dec. 6.
However, the 435-seat House of Representatives is still in the balance.
Republicans have the advantage, but votes are still being counted in several races, including many in liberal-leaning California.