The pro-Western president of Moldova, Maia Sandu, won re-election on Sunday in a high-stakes runoff vote in the former Soviet republic against a rival candidate she had denounced as “Moscow’s man.”

The vote — held a week after a contested election in Georgia, another former Soviet territory, handed victory to the Moscow-leaning governing party — has been closely watched by the United States, the European Union and Russia as a critical test of Moldova’s direction.

With more than 98 percent of ballots counted, official results gave Ms. Sandu 54.9 percent of the vote, an unassailable lead on her Moscow-friendly rival, who had 45.3 percent.

In a televised address early Monday, she thanked Moldovans living abroad, whose vote tipped the result in her favor, but said the election was a victory for the whole country. “Today you saved Moldova,” she said, “In our choice for a dignified future, no one lost.”

In an apparent reference to Russia, Ms. Sandu assailed “hostile forces from outside the country and criminal groups” for mounting a campaign to sway the result, which she said, citing “dirty money and illegal vote buying,” had been an “attack unprecedented in the whole of Europe’s history.”

European leaders celebrated the election as a victory against what Poland’s prime minister, Donald Tusk, described as “Russia’s aggressive and massive interference.” He expressed hope “that this trend will continue in the coming days and months in other countries as well.”