* Nineteen candidates in the race to replace Macky Sall

* No clear front-runner, momentum with opposition

* Months of turmoil shakes support for ruling coalition

DAKAR, March 21 (Reuters) - Senegal will hold its delayed presidential election on Sunday amid an unusually tense political mood after President Macky Sall failed to postpone the vote and two key opponents were released from prison, handing momentum to the opposition.

Support for Sall in Senegal, usually one of coup-prone West Africa's most stable democracies, has dropped during his second term in office, which will be his last. For the first time in the country's history, the incumbent will not be on the ballot.

The ruling coalition has picked Amadou Ba, 62, a former prime minister and finance minister as its candidate, who is likely to pursue Senegal's investor-friendly policies as it readies to become an oil and gas producer by the end of 2024.

But Ba faces a crowded opposition field of 18 candidates, the most prominent being 43-year-old former tax inspector Bassirou Diomaye Faye, who has been propelled to the frontline by support from firebrand opposition leader Ousmane Sonko.

Sonko, who is popular among urban youth frustrated with a lack of jobs and economic hardship, came third in the 2019 presidential race but was disqualified this time due to a defamation conviction. Both Sonko and Faye were released from jail on March 14 due to an amnesty proposed by Sall after months in detention, and have since drawn thousands to their rallies.

"The opposition has certainly gained momentum after the release of Faye and Sonko," said Mucahid Durmaz, senior West Africa analyst at risk intelligence company Verisk Maplecroft. "Sonko's charismatic and fiery presence is fuelling Faye's campaign."

Without any opinion polls, it is not clear whether any candidate will secure over 50% of the vote to prevent a runoff.

Faye, who was held on a defamation and contempt of court charge, promises to tackle inequality and corruption and has proposed monetary and institutional reforms, as well as renegotiation of oil, gas and mining contracts.

Durmaz said a Faye victory would see the state wield more power over the economy and resources. Although the pace of reforms would likely be moderate, it could tarnish Senegal's reputation as an attractive investment destination, he said.

MONTHS OF TURMOIL

Other politicians who could progress to a second round for the top two candidates include Khalifa Sall, 68, a former mayor of the capital Dakar and veteran politician Idrissa Seck, 64, who came second in the 2019 election with 21% of the vote.

Originally slated for Feb.25, the election was abruptly delayed by Sall on Feb. 3, only hours before campaigning was set to commence. He cited risks stemming from disputes over the candidate list as the reason for the postponement.

The decision triggered a wave of violence and led the country's highest constitutional authority, the Constitutional Council, to reject attempts to delay the vote and extend Sall's mandate beyond April 2.

The months of turmoil raised concerns of a backslide in one of the more stable democracies in a region that has seen eight military coups in three years.

Around 7.3 million people are registered to vote among Senegal's nearly 17 million, more than 60% of whom are under 25.

Mouhamadou Diallo, 25, a telecommunications engineer, said the next president should restore trust between the government and people, and tackle growing inequality.

"Life is excessively expensive, there are no jobs, and given our resources, there should be a fairer redistribution of wealth, so it is more equitable," Diallo, 25, said.

"There is a building on every street corner, yet I can't afford housing or even a plot of land. This kind of reality creates frustrations that you accumulate over time," he said.

(Reporting by Bate Felix and Ngouda Dione Editing by Alexandra Hudson)