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 is sitting on 48.7% of the vote – a narrow edge over Republican former state attorney general Adam Laxalt on 48.2%.
Ms Cortez Masto, 58, campaigned heavily on the issue of abortion and also criticised Mr Laxalt over his ties to major oil companies, which have enjoyed record profits in recent months.
Mr Laxalt had tried to tie Ms Cortez Masto to President Joe Biden’s economic policies, blaming them both for inflation and rising fuel prices.
The election result comes a day after Democrat Mark Kelly claimed victory in Arizona, beating his Republican challenger Blake Masters, who – like Mr Laxalt – had been endorsed by former president 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.