YAROSLAVL, RUSSIA - MARCH 14: Yaroslavl mayoral candidate Yevgeny Urlashov meets with voters at an outdoors get-together in the Dzerzhinsky district of the city in Yaroslavl, Russia on March 14, 2012. (Photo by Will Englund/The Washington Post) (Will Englund/THE WASHINGTON POST)

In an election that has been intensely watched as a marker for the future direction of Russian politics, an outsider running for mayor of Yaroslavl appeared to be headed for a landslide win Sunday night over the candidate backed by the ruling United Russia party.

A victory would give the opposition here a huge, national lift, just three weeks after the election of Vladimir Putin to the presidency demonstrated the continuing durability of the system he has constructed over the past 12 years.

And it presents the authorities — in Yaroslavl, a city of 600,000 about 160 miles northeast of Moscow, and in the Kremlin, as well — an unmistakable reminder that politics in Russia has become considerably more challenging since street protests broke out in September.

Late Sunday, Yevgeny ­Urlashov, 44, who ran against corruption and official arrogance, had 67 to 69 percent of the vote, with at least 60 percent counted. His opponent, Yakov Yakushev, the owner of a paint factory, trailed with about 29 percent — virtually the same percentage he polled in the first round of the elections on March 4. Urlashov got 40 percent in that round; two other candidates split the rest.

Yakushev did not run as an official United Russia candidate, but he had unlimited access to television and radio during the runoff campaign and was given a helping hand when the outgoing mayor appointed him as his deputy. Urlashov was forced to campaign in the courtyards of apartment houses.

A reported 1,000 observers fanned out across the city Sunday, watching for evidence of fraud. At least 60 complaints were recorded — mostly about Yakushev’s election workers. One report said Yakushev had called for the cancellation of the elections because of purported fraud. That would leave him, as deputy mayor, in charge of the city.

But Urlashov’s supporters believe that his overwhelming majority would make it impossible for those in power to take the election away from him.

Urlashov voters were motivated by “their infuriation with the unprecedented and impertinent attempts by the authorities to push their candidate into power,” said Pyotr Stryakhilev, a freelance journalist in Yaroslavl.

Assuming that Urlashov is sworn in as mayor, the big question facing him will be the degree to which United Russia and its allies try to thwart him — on the city council and at the regional level. To the extent that his opponents can make him fail, it will be seen as a failure of the democratic opposition.

But the Yaroslavl region is headed for gubernatorial elections, probably in the fall, to choose a replacement for the hugely unpopular, presidentially appointed incumbent. Those elections are part of a series of mild changes proposed by President Dmitry Medvedev in response to the political protests that erupted in Russia after parliamentary voting in December, although they were later watered down. Dominated by the city of Yaroslavl, the region could follow the city’s example and become a bulwark of opposition power.