Jamaican PM Portia Simpson Miller has said she "accepts" preliminary results of the country's general election, which give the opposition a lead.
The JLP has waited 18 years to get back into power
But Mrs Simpson Miller said her People's National Party (PNP) might still challenge some poll results.
A final count is under way, with Bruce Golding's Jamaican Labour Party (JLP) holding 32 of 60 seats in parliament.
Correspondents say the prime minister has been under pressure to concede, ending the PNP's 18 years in power.
Final results are expected on Thursday evening.
Earlier Mrs Simpson Miller, Jamaica's first female prime minister, said the poll had been marred by irregularities such as illegal campaigning and "vote buying".
She alleged that some candidates had campaigned beyond the official cut-off period, and said some of her party members were prevented from casting their ballots.
But in a statement posted on the PNP website on Tuesday evening, she said the party would accept the voice of the Jamaican people.
"The People's National Party accepts the announced preliminary results, while reserving all legal rights under the Jamaican constitution and our electoral laws," she said in the statement.
But the prime minister said nothing was certain until the final count was completed.
JLP General Secretary Karl Samuda responded to the PNP statement, telling The Gleaner newspaper that it was unfortunate Mrs Simpson Miller had "qualified" her concession.
There was a very close result in several constituencies
Three constituencies were decided by fewer than 100 votes, but some reports said these were from among the PNP's existing tally of 28 seats.
Any change in the result could increase the JLP's overall lead, they said.
Mr Golding has stopped short of claiming victory but has left no doubt that he thinks he will be forming the next government.
The voting itself was largely peaceful, but in the St Andrews area of Kingston shots were fired at a polling station from a car.
The two main parties do not differ significantly in ideology. Analysts say voters may have been looking for a change to tackle Jamaica's deep-seated poverty, 9% unemployment and a murder rate that is among the highest in the world.
The election had been scheduled for 27 August but was postponed for a week after Hurricane Dean swept across the island, causing widespread damage.