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. Korckok 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.