By Margarita Antidze and Thomas Grove
BAKU (Reuters) - Azerbaijan's President Ilham Aliyev looks certain to extend his rule in the oil-producing former Soviet republic for a third straight term in an election on Wednesday that opponents say has already been skewed in his favor.
In the decade since Aliyev succeeded his father, Azerbaijan has enjoyed a boom that raised living standards and has courted Western countries drawn by its strategic location and oil and gas reserves which it exports to European consumers.
But Aliyev, 51, has faced criticism at home and abroad over the government's treatment of dissenters in the nation of 9 million people, where protests are quickly quashed.
Polls opened at 8 a.m. (0300 GMT) with the singing of the Azeri national anthem, and voters began dropping their ballots into white boxes bearing the emblem of the Azeri flag.
Ali Takhmazov, a 66-year-old former politician, said he cast his ballot for Aliyev, because he had shown himself to be an effective leader.
"He has already proved that since 2003 he can lead the country and the first five years created a strong base for the second term and now we're looking at a third term. But let's see a fourth term, a fifth term, I don't see any alternative to him in the next 10-15 years," he said.
Aliyev, who could conceivably rule for life after backing a referendum that abolished term limits in 2009, hopes to increase Azerbaijan's regional clout in a new five-year term and gain control over a breakaway territory held by ethnic Armenians.
His biggest challenge, however, may be the dissent that has grown over what critics call endemic corruption, a gaping divide between rich and poor and alleged abuses in a nation where one rights group said a pre-election crackdown had doubled the number of political prisoners.
The number of protests has increased, sparked in part by young people using social media like Twitter and Facebook. Some in the predominantly Muslim nation with secular rule have taken inspiration from the Arab uprisings.
Rights groups say Azerbaijan's strategic location between Turkey, Russia and Iran, its Europe-bound oil and gas pipelines and its role as a transit route for U.S. troops to reach Afghanistan have cushioned it from Western criticism.
"Ahead of the presidential elections, Azerbaijan is trying to project an image of a country which respects human rights. But the reality could not be more different," Amnesty International said in a statement.
The opposition has united for the first time behind a single candidate, Jamil Hasanly, a 61-year-old historian. He said that, following a skewed pre-election campaign, he believed the poll would be rigged in favor of Aliyev.
"What we see is just an absence of a political and democratic climate for a free and fair election," Hasanly told a news conference on the last day of campaigning.
Opinion polls showed Aliyev far ahead in a field of 10 candidates. Opposition leaders have applied to Baku city authorities to hold a rally on Saturday, bracing for a potential defeat.
But few expect sustained protests after the vote, in which Aliyev's victory is a foregone conclusion for many who cite his control over most levers of power and the media.
Aliyev has dismissed accusations of human rights abuses and says Azeris enjoy full democratic freedoms, including a vibrant opposition press and free and fair elections.
He has benefited from the reputation of his father, Heydar, who led the country out of the economic chaos of the 1990s and a war over Nagorno-Karabakh, a mountainous territory controlled by ethnic Armenians. About 30,000 people were killed in the war.
Economic growth has slowed since Aliyev's first term, but he boasts that per capita gross domestic product increased to $7,850 in 2012 from $850 in 2003.
"I will vote for Aliyev because he has done a lot for our country... I don't want Azerbaijan to return to chaos and I don't trust the opposition at all," said Sabina Guluzade, 52, a schoolteacher in Baku.
Polls close at 7 p.m. (1400 GMT). First official preliminary results are expected within hours of polls closing.
(Editing by Alessandra Prentice and Mike Collett-White)