SAO PAULO — Organizers called off the final televised debate of Brazil's presidential election on Thursday after both frontrunners — leftist President Luiz Inacio Lula da Silva and right-wing Senator Flavio Bolsonaro — chose not to attend.

Mr. Bolsonaro, the eldest son of former President Jair Bolsonaro, had initially planned to take part in the TV Globo debate, the last major campaign fixture before Sunday's vote. He withdrew just hours before airtime after Lula, who has skipped every debate this year, declined to appear.

“My only opponent in this campaign is Lula,” Mr. Bolsonaro said this week. “He's the one I want to debate.”

In a statement, TV Globo said it canceled the event after receiving last-minute court rulings that altered the previously agreed debate rules, including restrictions on referring to absent candidates.

The cancellation underscores the declining role of televised debates in Brazilian politics — once a hallmark of the country's democracy after decades of military dictatorship — and leaves voters without a direct clash over policy just days before the first-round vote.

Lula, who has led every major poll ahead of Sunday's first round, has avoided sharing a stage with a field dominated by right-wing candidates capable of concentrating their attacks on him, as he sets his sights on a likely runoff against Mr. Bolsonaro.

“I don't go to debates to listen to nonsense. If the debate isn't helpful to the public, why should I go just to respond to trash talk?” Lula said in July.

Running for president for the seventh time, Lula also declined to participate in the last debate before the first round of his 2006 reelection campaign, a decision that drew widespread criticism at the time. Rivals have accused him of dodging scrutiny over his administration.

Four right-of-center candidates had been expected to take part in the TV Globo event: author-psychiatrist Augusto Cury, former Goias Governor Ronaldo Caiado, former Minas Gerais Governor Romeu Zema and Renan Santos. TV Globo is Brazil's largest free-to-air broadcaster.

Other networks had already canceled two additional debates after both frontrunners declined to attend. Rather than appear at Thursday's debate, Lula — who is seeking an unprecedented fourth non-consecutive term — was set to feature on a podcast at the same time the TV Globo event would have aired.

A Datafolha poll released Thursday showed Lula with 42% support for the round, ahead of Mr. Bolsonaro at 38%. In a simulated runoff scenario, the president would take 48% of the vote against the senator's 45%. Under Brazil's two-round electoral system, a runoff is held when no candidate wins more than 50% of valid votes in the first round.

— Reuters