By Orhan Coskun and Daren Butler
ANKARA (Reuters) - A second-time presidential candidate who lost out to Tayyip Erdogan in a 2018 vote could push Turkey's May election to a second round, potentially boosting the president's prospects of winning, according to analysts and polls.
Muharrem Ince, formerly of the main opposition Republican People's Party (CHP), joined the fray last month and secured a spot on the ballot at the weekend, fuelling concerns among Erdogan's opponents about a split in the opposition vote.
Some surveys put Ince's support at more than 5%, with one by Panoramatr giving him 10% last month.
Pollsters and analysts say his backers would mostly otherwise vote for CHP leader Kemal Kilicdaroglu, who is the main opposition candidate seen as the biggest electoral challenge to Erdogan in his 20 years in power.
"The fundamental consequence of Ince's (candidacy) is sending the elections to a second round," Panoramatr research director Osman Sert told Reuters.
He said Ince's support could slide from 10%, where it has mostly held over the last month, as the vote approaches. "But even if there is such a meltdown it would not prevent the election going to a second round," Sert said.
Some analysts say Ince might agree a deal with Kilicdaroglu and withdraw before the vote to boost the opposition which, polls suggest, retains an edge over the incumbent Erdogan.
But Ince indicated he would not bow to such pressure.
"There is no situation that would require us to withdraw and technically this isn't possible," he told broadcaster Haberturk on Monday, noting that an official draw on Saturday formalised his spot on the ballot.
Ince, whose blunt speeches and impromptu dances have drawn social media attention, resigned from the CHP two years ago and formed the Homeland Party after twice failing to become CHP leader.
"They are saying, 'Muharrem Ince, withdraw'," he said on Haberturk, referring to opposition critics. "Their only concern is, 'We'll lose the election, let's declare the guilty party now'."
A senior opposition party official, declining to be named due to the issue's sensitivity, said Ince's candidacy would make it difficult to defeat Erdogan in the first round but this can be overcome if, as the opposition alliance expects, his support and that of the fourth candidate Sinan Ogan drops to near 5% by election day.
A senior official from Erdogan's AK Party said its internal polls put Ince's support at some 8-9%, but did not provide the data.
If no presidential candidate gets more than 50% in the May 14 vote, the top two would compete in a second round two weeks later. Voters will also select parliamentarians.
Analysts say that whichever alliance - ruling or opposition - controls parliament will be well placed for its candidate to win a second presidential round given they could campaign on stability. Polls indicate the AKP will remain the largest party in parliament.
Data from closely-watched pollster Metropoll showed Ince and undecided voters would determine the presidential vote, its head Ozer Sencar said.
In its March survey, 44.6% of respondents said they would vote for Kilicdaroglu and 42.0% for Erdogan, if just given a choice between the two, while nearly 6% planned a "protest" vote.
Erdogan was 2.9 points ahead in a similar January survey by Metropoll.
Support for Erdogan dipped after February's devastating earthquake amid perceptions of an initially slow response. More than 50,000 people were killed and millions left homeless.
Among voters opposed to Erdogan, some voice dissatisfaction with the diverse main opposition alliance, partly as it includes parties led by former Erdogan allies and an Islamist party.
"The fact that these people would be ministers and come to positions of authority bothers me," said 28-year-old student Seckin Yetkin, saying he will vote for Ince like in 2018.
Ince won 30.6% of that vote, behind Erdogan on 52.6%.
(Additional reporting by Jonathan Spicer and Ezgi Erkoyun; Writing by Daren Butler; Editing by Jonathan Spicer, William Maclean)