Georgians are voting on Sunday for a president to succeed Mikheil Saakashvili, who during almost a decade in power has turned the former Soviet republic into a fledgling democracy and a staunch US ally.

For Saakashvili, it is a bitter departure. The vote is expected to cement the control of his rival, billionaire prime minister Bidzina Ivanishvili, whose coalition routed the outgoing president's party in a parliamentary election a year ago.

Ivanishvili's chosen candidate, Georgi Margvelashvili, a former university rector with little political experience, is expected to win Sunday's election.

Ivanishvili has promised to step down next month and nominate a new prime minister, who under Georgia's new parliamentary system will acquire many of the powers previously held by the president.

Ivanishvili has yet to name his choice. He also says he intends to maintain influence over the government, although how is not entirely clear. But his fortune, estimated at $5.3bn (£3.3bn), gives him considerable leverage in a country with a gross domestic product of $16bn.

Much uncertainty also hangs over the future of Saakashvili. Since last year's parliamentary election and what was in effect a transfer of power, dozens of people from his team, including several former ministers, have faced criminal charges and some have been jailed, including the former prime minister.

Ivanishvili says prosecutors are likely to question Saakashvili as well once he has left office.

In Sunday's election, Saakashvili's party needs its candidate, David Bakradze, a former parliamentary speaker, to finish a strong second among the 23 candidates to maintain political influence.

While Ivanishvili made his money in Russia and has had some success in restoring trade ties with Georgia's hostile neighbour, he has maintained the pro-western course set by Saakashvili.

"Nobody can change this. This is the will of the Georgian people, to see their country in the EU and in Nato," said Alexi Petriashvili, one of Ivanishvili's ministers. "The majority see the US as Georgia's strongest strategic partner."

If not for Washington, Georgia most likely would not have survived as an independent state, Petriashvili said in an interview with the Associated Press. He pointed specifically to Washington's support for the closure of Russian military bases there in 2005.

The US supports Georgia diplomatically and financially, with assistance in 2013 totalling about $70m.