Updated

Progressive challenger Cori Bush defeated longtime incumbent Rep. William Lacy Clay overnight in the high-profile Democratic primary in Missouri's 1st Congressional District -- a race that grabbed national attention as a party fixture and Congressional Black Caucus member tried to fend off a younger activist who came up through the Black Lives Matter movement.

Bush's 48.9% to 45.5% victory is yet another win for Justice Democrats, the group that backed the successful Democratic primary challenges by Rep. Alexandria Ocasio-Cortez over longtime Rep. Joe Crowley in 2018,  and educator Jamaal Bowman over powerful Rep. Eliot Engel this summer.

“They counted us out,” Bush said after her Tuesday win. “They called me — I’m just the protester, I’m just the activist with no name, no title and no real money. That’s all they said that I was. But St. Louis showed up today.”

The 10-term Clay was defending a seat that’s been represented by his family for more than half a century. The incumbent succeeded his father – the late Rep. William Clay Sr. – who held the St. Louis-area seat for more than 30 years and was one of the founders of the Congressional Black Caucus.

ST. LOUIS PROSECUTOR WHO CHARGED COUPLE FOR DISPLAYING WEAPONS WINS DEMOCRATIC PRIMARY

The 64-year old Clay's was facing a second straight primary challenge from Bush, a nurse who enjoyed the backing of some of the biggest names on the left.

'From the Bronx to St. Louis, the Squad is here to stay, and it's still growing.'

— Justice Democrats

Bush, who is also Black, lost to Clay two years ago by double digits. In her second challenge to Clay, she was endorsed earlier this year by then-presidential candidate Sen. Bernie Sanders of Vermont. And she recently landed the backing of Bowman.

Justice Democrats, which was founded in 2017, noted that Bush was one of the first-ever candidates it backed.

CUOMO BEATS BACK 'SURPRISE' AOC CHALLENGE TO LEAD NY DELEGATION TO DNC

"From the Bronx to St. Louis, the Squad is here to stay, and it's still growing," the organization tweeted early Wednesday morning.

Bush’s campaign spokeswoman, Keenan Korth, said voters in the district were “galvanized.”

“They’re ready to turn the page on decades of failed leadership,” Korth said.

The 44-year old Bush gained momentum as the primary neared. The ordained minister who says she got involved in politics as a Black Lives Matter activist in the wake of the 2014 fatal police shooting of Michael Brown in Ferguson, Mo., raised nearly $240,000 in the spring, including $170,000 in June alone. That was a major increase in her fundraising compared with the prior 14 months of her campaign.

CLICK HERE TO GET THE FOX NEWS APP

Both candidates embraced progressive policies and civil rights legislation.

Bush will now be considered the clear favorite in November's general election in a distict that overwhelmingly favors Democrats.