Unofficial results from Senegal's presidential election suggest a tight race between incumbent Abdoulaye Wade and former Prime Minister Macky Sall.A source in the electoral commission has told the BBC that a run-off between the pair is "likely", backing local media reports and Mr Sall's comments.President Wade, 85, is seeking a third term in office despite serving a constitutional limit of two terms.Mr Wade was booed as he cast his vote on Sunday in the capital, Dakar.They could be heard shouting: "Get out, old man!"Mr Wade's decision to stand again has sparked weeks of violent protests - leading to about six deaths - although polling day itself was largely peaceful.Early reports indicate that Mr Wade and Mr Sall have each won between 20-35% of votes - more than any of the other 12 candidates.The electoral commission has yet to publish any provisional results, which are being announced by local media as they trickle in from polling stations.The source said the first results should be published later on Monday.Mr Wade lost in his own constituency in the middle-class Dakar neighbourhood of Point E, Senegal's national APS news agency reports.Mr Wade's spokesman Serigne Mbacke Ndiaye told the BBC he remained confident of a first round victory as the president is "well ahead".But Mr Sall believes that "a second round is inevitable, we have won the biggest departments in the country."The 50-year-old geologist and mayor of the western town of Fatick, who is running for the first time, also warned against rigging.The BBC's Thomas Fessy in Dakar says Mr Sall has been the only opposition candidate to run a real electoral campaign around the country, as other leaders struggled to mobilise people in street protests.If a run-off is confirmed, an "anyone but Wade" coalition could emerge behind Mr Sall, our correspondent says.Senegal's constitutional court ruled that Mr Wade could stand again on the grounds that his first term had not counted since it began before the two-term limit was introduced in 2001.The court also barred world-famous singer Youssou N'Dour from standing in the election.Mr N'Dour has argued that allowing Mr Wade to run again amounts to a constitutional coup d'etat.Senegal, a former French colony, is seen as a stable democracy with an unbroken series of elections since independence in 1960.