Voters in Slovakia on Saturday strengthened the grip of Russia-friendly political forces in Central Europe, handing victory in a presidential election to a candidate who opposes providing military and financial aid to Ukraine.

With 99 percent of the votes counted, the official tally showed Peter Pellegrini, an ally of Slovakia’s populist prime minister, Robert Fico, the winner with 53 percent of the vote in a presidential runoff. Despite the presidency’s limited powers in Slovakia, the election was widely watched as a test of strength between political camps with starkly different views on Russia.

The defeated candidate, former Foreign Minister Ivan Korcok, is a stalwart supporter of Ukraine and critic of Mr. Fico, a pugnacious veteran politician who has aligned with Prime Minister Viktor Orban of Hungary in opposing aid to Ukraine and challenging mainstream opinions within the European Union.

With Mr. Fico at his side, Mr. Pellegrini declared victory early Sunday, soon after Mr. Korcok conceded defeat.

Mr. Korcok came first among nine candidates in an initial round of voting on March 23, but he lost in Saturday’s face-off with Mr. Pellegrini, who appears to have picked up votes that in the first round went to an anti-NATO nationalist who finished third.

In the campaign leading up to the vote, Mr. Pellegrini copied tactics used by Mr. Orban during an election in 2022 in Hungary, in which his governing party falsely claimed that the main opposition leader wanted to send Hungarian soldiers to fight against Russia in Ukraine. Mr. Pellegrini used the same smear against Mr. Korcok, casting him as a warmonger intent on sending Slovak troops into Ukraine.

Mr. Korcok insisted that he had no such plan — which is not something a Slovak president has the power to carry out, anyway — but he had trouble breaking through a miasma of disinformation pumped out by pro-Russia websites and social media accounts.

His defeat is a big boost for Mr. Fico, who can now pursue his agenda without interference from the presidency. That is a marked shift from the tenure of the departing president, Zuzana Caputova, an outspoken, pro-Western liberal who used her limited powers to resist Mr. Fico’s drift toward Russia and his efforts to limit the judiciary’s ability to prosecute corruption. She did not run for a new term, saying that she was exhausted “from the professional and human point of view.”

Restrained by Ms. Caputova, Mr. Fico refrained from confronting fellow leaders over Ukraine during European Union summits in Brussels. The election of Mr. Pellegrini, however, could lead to a more confrontational approach like that of Hungary, the European bloc’s inveterate dissident.

In public statements, Mr. Fico has joined Mr. Orban in pushing for what he describes as “peace” in Ukraine, arguing that the war will drag on indefinitely without a swift negotiated settlement. Ukraine and its Western backers consider an end to the war impossible unless Russia gives up occupied territory.

Mr. Korcok, a career diplomat who served as Slovakia’s ambassador to Washington from 2018 to 2020, has dismissed calls for immediate “peace” as a surrender to Russia’s goal of hanging on to Ukrainian land. He supports the stance that providing military and financial support to Ukraine is the only way to bring a lasting end to the conflict.

Mr. Fico, a veteran politician who ended an earlier stint as prime minister by resigning in 2018 amid a swirl of corruption accusations, has also followed Mr. Orban in trying to neuter the judiciary and in casting supporters of Ukraine as disloyal lackeys of the United States.

Mr. Fico returned to power after a general election in September, reviving a political career that many had considered over when he quit amid large street protests after the killing of an investigative journalist who had been looking into government graft.

Pavol Strba contributed reporting from Bratislava, Slovakia.