Boston City Council At-Large Candidate Julia Mejia has prevailed for the fourth-place spot for the Council’s four at-large seats after a three-day-long recount.

According to the newest tally, certified Monday by the city’s Board of Election, Mejia won out over her closest opponent, Alejandra St. Guillen, by one vote.

The final tally was announced shortly after 6 p.m., and after lawyers for both candidates made final arguments over a handful of contested ballots — arguments that could presumably have swayed the outcome of the election.

The Board of Election voted to allow one ballot that had previously been rejected and not to allow another one. It is not clear which, if either, candidate those ballots favored.

Upon hearing the announcement, an emotional Mejia embraced supporters and family, and said the outcome shows that every vote matters.

St. Guillen, who had left to pick up her son from daycare, was not present at Boston City Hall when the results were announced. St. Guillen could decide to contest the outcome in court.

Neither state nor city laws provide for automatic recounts, no matter how close the margin of an election. Instead, candidates must petition the city for recounts ward by ward — for each of the city's 22 wards — by submitting at least 50 resident signatures from each ward the candidate wishes recounted.

Both Mejia and St. Guillen petitioned for citywide recounts after unofficial results released late on Election Night showed St. Guillen just 10 votes behind Mejia from winning the Council's fourth at-large seat.

Later vote tallies showed Mejia ahead by just five votes, and then eight votes by last count at the time the recount began.

Despite weeks of uncertainty over who would take the Council seat, one outcome became clear on Election Night: the Council would see its first Latina member with either candidate.

The recount marked the first citywide recount since 2001, when City Council At-Large Candidate Felix D. Arroyo emerged as the fifth-place vote-getter ahead of opponent Robert Consalvo by just over 60 votes after initially trailing Consalvo by 33 votes.