TOKYO — An anti-nuclear candidate’s victory in the Niigata gubernatorial race Sunday is a hammering blow to Tokyo Electric Power Co. Holdings, which hoped to quickly restart nuclear reactors and improve its finances.

Ryuichi Yoneyama, who opposes a restart of the Nos. 6 and 7 reactors at Tepco’s Kashiwazaki-Kariwa power plant in the prefecture, beat a candidate seen as more receptive to the plan. A Kyodo News exit poll showed 64% of voters were against the restart, and that many of them voted for Yoneyama.

Yoneyama has pledged to uphold the policy of outgoing Gov. Hirohiko Izumida, who has been cautious about restarting the reactors. Yoneyama, who ran as an independent, received backing from the Japanese Communist Party and the Social Democratic Party, both of which call for a Japan free of nuclear energy.

The Ministry of Economy, Trade and Industry — charged with nuclear power policy — and the Tokyo utility had hoped for a victory by rival Tamio Mori. Tepco is banking on the financial boost from a restart at Kashiwazaki-Kariwa to exit government control, which began in 2012 after the Fukushima nuclear disaster.

“That Yoneyama, who promised to honor Izumida’s policy, has been elected has serious implications,” said a METI official, adding that the ministry will “strive to build support with the new governor by listening to his opinion.”

“The people have spoken,” said Tepco through a spokesperson. “We will continue to bolster safety measures based on the lessons gleaned from Fukushima.”

Japan’s Nuclear Regulation Authority is at the final stage of inspecting the reactors for restart. Tepco’s decision to relocate the plant’s accident response center has made the date of approval uncertain, but the green light could come early next year.

Delays in resuming operations would damage Tepco’s hopes of rebuilding its finances, and likely also would impact discussions of how it can shoulder additional costs involving the Fukushima accident. Tepco promises to pay in principle the enormous cost of dismantling the damaged reactors, but that pledge now seems increasingly unrealistic.

With public opinion staunchly against nuclear power plants, plans to have the government or other utilities shoulder the cost are unlikely to win support. Japan hoped to reach a conclusion by year’s end, but that time frame, too, is now uncertain.