PORT-AU-PRINCE, Haiti - Government-backed candidate Jude Celestin and former first lady Mirlande Manigat will advance to a second-round vote in the race for Haitian president, the provisional electoral council announced Tuesday, as merchants in the capital prepared for possible riots.

But the matter might not be settled. The preliminary results from the Nov. 28 election have popular carnival singer Michel "Sweet Micky" Martelly trailing Celestin by about 6,800 votes -- less than 1 per cent.

The head of the joint Organization of American States-Caribbean Community mission has said that officials could consider putting a third candidate in the runoff if the vote is nearly tied.

Martelly had said that he would not accept a spot in a run-off in which Celestin is present. His campaign had no immediate comment and called a late Tuesday night press conference.

An appeals period runs through Dec. 10, with final results expected to be announced around Dec. 20. The run-off is scheduled for Jan. 16.

Turnout in the presidential race was low: Just over a million people cast accepted ballots out of some 4.7 million registered voters.

Officials acknowledged the rolls were both "bloated" and "incomplete," with hundreds of thousands of earthquake dead still registered and many living voters either still waiting for ID cards or being turned away at the polls amid confusion.

Manigat, a 70-year-old law professor, is the wife of a former Haitian president who served briefly after a much-criticized election before being deposed by a coup. Her supporters include a powerful senator who organized violent protests in his home department ahead of the first round of voting.

Celestin, a virtual unknown before the election, is the candidate of outgoing President Rene Preval's Unity party. He is the head of the state-run construction company whose trucks carted bodies and limited amounts of rubble out of the city after the Jan. 12 quake.

His campaign was the best-funded of the group but Preval's inability to jump-start a moribund economy or push forward reconstruction after the massive Jan. 12 earthquake drained his support. Many voters said they would accept "anyone but Celestin," who they equated with the unpopular Preval.

Twelve of the 19 candidates on the ballot joined to allege that fraud was used to ensure a Celestin victory and call for the cancellation of the vote. Manigat and Martelly were among them but later reversed position when officials remarked they had a chance to win.

Martelly, a popular carnival singer, was a dark horse who gained widespread credibility in the days before the vote. Thousands of his supporters took the streets of Port-au-Prince and Cap-Haitien while polls were still open, many believing he had won the race.

Bonfires were burning near the Petionville restaurant where the results were announced Tuesday and professed Martelly supporters threw rocks at people passing nearby after the vote was announced.

The much-anticipated results were released by council president Gaillot Dorsainvil around 9 p.m., three hours after a press conference was scheduled to begin.

As the hour approached merchants and residents in the capital prepared for a riot, covering market stalls and jamming streets to rush home. Some barricades were set up in the city.

Dorsainvil read slowly through all legislative results, one by one, before revealing the presidential tallies. The clear winner in the bid for senate seats was President Rene Preval's Inite, or Unity party, which advanced to a run-off in nine races and won a tenth. An independent candidate won the 11th.

The election was criticized by candidates for rampant disorganization, incidents of fraud and violence. In the last days of counting tabulators had to sort out clearly fraudulent tally sheets. U.N. Secretary-General Ban Ki-Moon said the problems were worse than originally reported.

But the U.N. peacekeepers and OAS-Caricom mission observer mission said the problems did not invalidate the vote.