PHOENIX (AP) - Democratic Rep. Kyrsten Sinema has won Arizona's open U.S. Senate seat, beating Republican Rep. Martha McSally.

Sinema will be Arizona's first female U.S. senator. She will also be the first openly bisexual U.S. senator in the nation's history. 

Sinema thanked her supporters in a tweet, saying she'll be an "independent voice for all Arizonans" in the U.S. Senate.

Sinema is expected to speak from the Montelucia resort in Scottsdale at around 6:30 p.m.

McSally has conceded in a video on Twitter, saying she has called Sinema to congratulate her.

Republican Sen. Jeff Flake, whose seat Sinema won, congratulated Sinema on Twitter and commended Martha McSally for a gracious concession speech. 

Arizona Gov. Doug Ducey tweeted his congratulations to Sinema and also to McSally on their historic campaigns.

The race between Sinema and McSally was one of the most closely watched in the nation. Sinema was declared the winner Monday as her lead grew insurmountable during Arizona's lengthy vote-count.

Sinema is a former liberal activist who became a centrist member of Congress. Her win follows years of Democratic shutouts at the statewide level in Arizona and shows that the longtime Republican bastion is becoming a swing state.

McSally hammered Sinema over her former liberal stances and claimed she was pretending to be a centrist

Sinema criticized McSally's vote to repeal the Affordable Care Act and kept her distance from national Democrats.

12 News also contributed to this report.

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