Republican J.D. Vance, the best-selling "Hillbilly Elegy" author backed by former president Donald Trump, won a contentious race for Ohio's open US Senate seat Tuesday, networks projected, in a disappointment for Democratic President Joe Biden.

The win for the Republicans does not represent a gain of a seat in the 100-member Senate, as Vance and rival Tim Ryan, a Democratic congressman, were vying to replace retiring Republican Rob Portman.

But it marks a failure of Biden's Democrats to flip a competitive seat in the all-important battle for control of the Senate, which is currently evenly split but held by Democrats because of Vice President Kamala Harris's tie-breaking vote.

And it keeps Republican hopes alive of wresting control of the upper chamber from the opposing party in Tuesday's midterm elections.

ABC and NBC both called the Ohio contest in Vance's favor. With 93 percent of votes in and counted, he was ahead of Ryan by more than seven points.

Vance, 37, earned national attention -- and acclaim -- in 2016 with his memoir about his modest and chaotic childhood in a working-class town in Ohio that has become a symbol of the industrial decline of the American Rust Belt.

A military veteran who became a venture capitalist in California, Vance entered politics last year and won his party's primary by drawing close to Trump, with whom he has had a topsy-turvy relationship.

Trump -- always keen on burnishing his own brand -- mocked the candidate at a September rally in Ohio, saying "J.D. is kissing my ass he wants my support so bad."

Despite the humiliation, Vance welcomed Trump back to the Midwestern state Monday for a rally in Dayton on the eve of the election.

Vance's fealty to Trump in red-leaning Ohio helped him remain competitive in the Senate race against Ryan, a working-class Democratic congressman who has kept his distance from Biden.

© Agence France-Presse