Official results yesterday showed the Union for the Development of the Comoros (UPDC) led by President Ikililou Dhoinine winning eight seats, followed by Sambi's Juwa with seven seats.
The remaining seats were divided between four different parties and one independent candidate.
The election was seen as a face-off between Juwa and Dhoinine, whose five-year term ends in May 2016.
Sambi, who was president between 2006 and 2011, is widely reported to be preparing for a comeback in the 2016 vote.
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The current administration has leaned more openly on former colonial power France.
After about twenty coups or attempted coups in the four decades since independence in 1975, Comoros' constitution was changed to rotate the presidency between the country's three islands.
Since 2009, the archipelago has enjoyed stability but Sambi's plans to seek reelection - even though it will not be his island's turn yet to hold the post - has sparked fears of renewed instability.
The second round runoff drew an "unprecedented" 73.05 per cent turnout, according to the electoral commission.