The Democrats will keep control of the US senate after a projected win in the state of Nevada, according to US media reports.
Democrat incumbent Catherine Cortez Masto looks set for a narrow victory over her Republican rival, former state attorney general Adam Laxalt.
It comes a day after Democrat Mark Kelly claimed victory in Arizona, beating his Republican challenger Blake Masters, who – like Mr Laxalt – was endorsed by Donald Trump.
This means the Democrats have 50 seats in the senate.
Democrat vice president Kamala Harris can break ties in the 100-member chamber, meaning that the party can secure victories for President Joe Biden.
This will be particularly important if a seat on the US Supreme Court, which currently has a 6-3 conservative majority – were to open up in the final two years of Mr Biden’s term.
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The final state to decide is Georgia, where Democratic senator Raphael Warnock faces a run-off against Republican Herschel Walker on 6 December.
The 435-seat House of Representatives remains in the balance, however.
The Republicans have the edge but votes are still being counted in several races, including many in liberal-leaning California.