* Victory for PM-backed Masuzoe was widely expected
* Anti-nuclear former PM Hosokawa takes 3rd place
* Nationalist former air force chief takes fourth
* Anti-nuclear power vote split (Recasts with election results)
By Linda Sieg
TOKYO, Feb 9 (Reuters) - A candidate backed by Prime Minister Shinzo Abe won Sunday's election for governor of Tokyo, frustrating a rival's efforts to make the vote a referendum on the Japanese leader's pro-nuclear energy policy nearly three years after the Fukushima disaster
The widely-expected victory by former health minister Yoichi Masuzoe comes as a relief for Abe, who had suffered a rare setback in another local election last month.
The 65-year-old Masuzoe, backed by Abe's Liberal Democratic Party, was the winner by a wide margin, according to media exit polls. Even before most votes were counted, Masuzoe's opponents conceded defeat.
The winner's most prominent rival was former prime minister Morihiro Hosokawa, 76, who came out of retirement to run and - with support from charismatic ex-premier Junichiro Koizumi - had put opposition to atomic energy at the core of his platform in the race to lead the capital city of 13.3 million people.
Hosokawa came in a close third after lawyer Kenji Utsunomiya, who also opposes nuclear power, NHK public TV said. A half-hour before the polls closed, turnout was a mere 34 percent, well below recent polls, the broadcaster said.
"I will make Tokyo the world's No. 1 city," Masuzoe told supporters. "I want to work on social welfare, disaster preparedness, the economy and especially to make the Tokyo 2020 Olympics a success."
Masuzoe had not made energy policy a prime focus, although he said Japan should reduce its dependence on nuclear power in the medium to long term. After his victory was announced, he reiterated that stance, adding he wanted to raise the share of renewable energy sources in Tokyo's electricity supply.
Public trust in nuclear energy in Japan was battered by the March 2011 disaster at Tokyo Electric Power Co Inc's Fukushima nuclear power plant north of Tokyo, triggered by an earthquake and tsunami. It was the world's worst nuclear accident since Chernobyl in 1986.
Surveys have shown that most Japanese voters favour abandoning nuclear power, either immediately or in the longer term, but they also indicate that energy policy is not as important an issue for voters as jobs and the economy, an ageing population and welfare.
However, Masuzoe's win is unlikely to mean smooth sailing for Abe's efforts to restart reactors shut down after the Fukushima accident. This is because of delays in safety checks by a new atomic regulator and the need to persuade host communities to agree to the government's plans.
Hosokawa opposed Abe's plans to make nuclear power a core source of energy and to restart the reactors.
Addressing supporters, Hosokawa said he felt there was a gap between the results and the enthusiasm he felt on the campaign trail.
"I am very sorry that my efforts were insufficient and that I could not meet the expectations of those who supported me so earnestly," he said.
Some anti-nuclear activists had urged Hosokawa and Utsunomiya, who was backed by the Japanese Communist Party, to join forces to avoid splitting the anti-nuclear vote.
Hosokawa led an anti-LDP coalition that briefly ousted the long-ruling party in 1993 for the first time in nearly four decades, but he quit the next year over a financial scandal.
Koizumi, 72, was one of Japan's most popular leaders during his 2001-2006 term and was once Abe's mentor.
Both ex-premiers supported nuclear power while they were in office but changed their stance after the Fukushima disaster.
Former air force chief of staff Toshio Tamogami, who resigned in 2008 after denying in an essay that Japan was the aggressor in World War Two, came in fourth. The pro-nuclear power Tamogami heads the nationalist group "Gambare Nippon!" ("Stand Firm! Japan").
The election was held to replace Naoki Inose, who resigned in December over a financial scandal. (Editing by William Mallard and Richard Borsuk)