CHICAGO — Democrats are now all but certain to elect another Black woman to the U.S. Senate after Lt. Gov. Juliana Stratton won Tuesday’s bitter and expensive primary in Illinois.

Stratton overcame a crowded Democratic contest for the state’s open Senate seat, defeating front-runner Rep. Raja Krishnamoorthi with the help of millions of dollars of outside spending — much of it from her old running mate, Gov. JB Pritzker.

She is widely seen as the favorite to succeed Sen. Dick Durbin in the blue state and would become the sixth Black woman to have ever served in the upper chamber.

The contest was defined by heavy outside spending and intraparty fissures over race. It became contentions during the final weeks, with Krishnamoorthi and Stratton trading sharp attacks on the debate stage and blasting each other in TV ads over corporate money and immigration policy.

Members of the Congressional Black Caucus — who backed a different contender, Rep. Robin Kelly, in the primary — also warned that Pritzker’s interference could split the Black vote and cost Democrats a chance at electing a Black woman to the Senate this year.

Stratton’s late surge was powered by a combination of endorsements, outside spending and targeted messaging. She benefited from the support of Pritzker and Sen. Tammy Duckworth (D-Ill.). Illinois Future PAC, which received major cash infusions from Pritzker and other allies, spent at least $11.8 million boosting Stratton’s campaign and attacking Krishnamoorthi.

Stratton will face Don Tracy, a former Illinois Republican Party chair, in November. If elected, she would become the second Black woman to be nominated to the Senate from Illinois, following Carol Moseley Braun — who endorsed Stratton in the contest.