Incumbent Democrat Mark Kelly defeated Republican Blake Masters on Friday to win a US Senate seat in Arizona, a contest that left Democrats one seat short in the battle for control of the chamber with two more races to be decided.

The win by Kelly, a former astronaut whose wife, Gabby Giffords, survived an assassination attempt when she was a US lawmaker, meant Democrats had battled to a 49-49 tie in the race for the Senate.

"I'm humbled by the trust our state has placed in me to continue this work," Kelly said on Twitter.

Control of the Senate - and the shape of President Joe Biden's next two years in office – will now hinge on contests in Nevada and Georgia. Biden's party avoided historical trends by limiting their losses in Tuesday's midterm elections, shocking Republicans who had expected big gains.

Democrats needed one more seat for control, since Vice President Kamala Harris can cast the tie-breaking vote.

In Nevada, incumbent Democratic Senator Catherine Cortez Masto had closed to within about 800 votes of the Republican state attorney general, Adam Laxalt. Georgia's outcome is weeks away as Democratic incumbent Senator Raphael Warnock will face Republican Herschel Walker in a December 6 runoff.

In the Nevada governor's race, Republican Joe Lombardo defeated Democrat Steve Sisolak, Edison Research projected. Sisolak conceded the race.

"Whether you voted for me or Sheriff Lombardo, it is important that we now come together to continue moving the state forward," Sisolak said in a statement posted on Twitter. "That is why I reached out to the sheriff to wish him success."

Political analysts anticipate a rush of campaign funds into Georgia as Republicans and Democrats gear up for the final battle of the 2022 midterm elections. (Reuters)