Democratic Senator Mark Kelly won his bid for re-election in the crucial swing state of Arizona, defeating Republican venture capitalist Blake Masters to put his party one victory away from clinching control of the chamber for the next two years of Joe Biden’s presidency.

With Vice President Kamala Harris’ tiebreaking vote, Democrats can retain control of the Senate by winning either the Nevada race, which remains too early to call, or next month’s runoff in Georgia.

Republicans now must win both those races to take the majority.

The Arizona race is one of a handful of contests that Republicans targeted in their bid to take control of the 50-50 Senate.

It was a test of the inroads that Kelly and other Democrats have made in a state once reliably dominated by the Republicans.

Mr Kelly’s victory suggests Democratic success in Arizona was not an aberration during Donald Trump’s presidency.

Other Arizona contests, including the closely watched race for governor between Democrat Katie Hobbs and Republican Kari Lake, were too early to call Friday night.

Mr Kelly, a former Nasa astronaut who has flown in space four times, is married to former US Representative Gabby Giffords, who inspired the nation with her recovery from a gunshot wound to the head during an assassination attempt in 2011 that killed six people and injured 13.

Mr Kelly and Ms Giffords went on to co-found a gun safety advocacy group.

Election 2022 Arizona Senate
Blake Masters (Matt York/AP)

Mr Kelly’s victory in a 2020 special election spurred by the death of Republican Senator John McCain gave Democrats both of Arizona’s Senate seats for the first time in 70 years.

The shift was propelled by the state’s fast-changing demographics and the unpopularity of Mr Trump.

Mr Kelly’s 2022 campaign largely focused on his support for abortion, protecting Social Security, lowering drug prices and ensuring a stable water supply in the midst of a drought, which has curtailed Arizona’s cut of Colorado River water.

With President Joe Biden struggling with low approval ratings, Mr Kelly distanced himself from the president, particularly on border security, and played down his Democratic affiliation amid angst about the state of the economy.

He also styled himself as an independent willing to buck his party, in the style of Mr McCain.