In a rare defeat, United Russia lost a weekend election, with a Communist rival trumping a candidate from the ruling party who had refused to participate in public debates.
Communist candidate Ilya Potapov scored 59 percent in the second round of elections in the Novosibirsk regional town of Berdsk, Interfax said. United Russia-backed incumbent Mayor Vladimir Shtop won 37 percent.
Nearly 43 percent of registered voters in the town of 96,000 came to the polls, the report said.
Of the initial six mayoral candidates, Shtop was the only one who refused to participate in a debate organized by a local newspaper on March 3, Vedomosti reported Thursday.
United Russia candidates often refuse to debate opponents before elections, following the lead of Vladimir Putin and Dmitry Medvedev, who both rejected offers to debate rivals during presidential elections that they easily won in the first round of voting.
But Shtop had a change of heart after collecting 37 percent in the first round on March 13, forcing a runoff with Potapov, who won 30 percent. He invited Potapov to a debate, which took place Thursday, said the newspaper Kuryer-Sreda-Berdsk, which organized the event.
Potapov pledged on Monday not to join United Russia like many other politicians have done after defeating ruling party candidates in local elections in recent years.