They will battle over the role of public employee unions. They'll debate the city's treatment at the hands of Beacon Hill. And each will tread delicately around the legacy of Mayor Thomas M. Menino, who remains popular but is not particularly fond of either of them.
Perhaps most fundamentally, Representative Martin J. Walsh of Dorchester and Councilor John R. Connolly of West Roxbury turn now to a general election that will force them to wrestle over the city's geographic middle.
By dint of hailing from one of the city's easternmost precincts and one of its westernmost, Walsh and Connolly will need to compete for the yawning valley of voters in the center of the map, angling for supporters of candidates who were eliminated in Tuesday's preliminary. Well more than half of the votes cast are up for grabs, given that they were cast for candidates no longer in the race.
And, because Walsh and Connolly come from the same ethnic tribe, they must also jockey to appeal to voters of color, many of whom expected that more than a decade since the Census showed a majority-minority population would be enough time for a nonwhite mayoralty to assert itself.
"Communities of color will be the battleground turf, and it's going to be over who is going to speak most compellingly to those communities," said state Senator Sonia Chang-Diaz, a Jamaica Plain Democrat who endorsed Charlotte Golar Richie. The former state representative placed third on Tuesday.
The Walsh-Connolly pairing will provoke some soul searching among political types in those communities. In a city where whites have been outnumbered by people of color for 13 years, and where white voters have demonstrated willingness to vote for candidates of color for a series of election cycles, why were three solid candidates — Felix Arroyo, John Barros, and Golar Richie — unable to break through?
Menino's tarrying before announcing his decision to step down played a role. Weighing his health problems against his desire to continue governing the city, the mayor waited until late March before making his intentions known. That compressed the election cycle, which played to the advantage of established political figures with existing political organizations and campaign accounts that already showed hardy balances.
Neither Walsh nor Connolly fits neatly into the "Old Boston" mold hinted by their common ethnicity.
Connolly, for instance, cleverly teamed in 2011 with Ayanna Pressley, fellow at-large councilor, helping usher Pressley back onto the council and burnishing Connolly's credentials as a forward-looking, bridge-building member of the city's next political generation.
Walsh was blistered by conservative forces in his heavily Catholic, southeastern Dorchester district for voting in favor of gay marriage, but has since called it the vote of which he is most proud.
On the campaign trail this year, he has touted a program he organized as head of the Building and Construction Trades Council to connect women and minority workers with industry employers.
With an eye on the city's decades-long, seemingly inexorable march toward a more ethnically diverse and ideologically liberal electorate, both men have been working to expand their natural core of supporters.
And if, as some political observers suggest, ethnicity has faded as a central issue in Boston elections, then neither man would be hard pressed to stretch beyond the traditional ethnic power bases before November.
"We have a stake in this as well, and it's up to all of us to come out regardless of our skin color, and regardless of our ethnic background," said state Representative Jeffrey Sanchez, who remained neutral during the preliminary.
Nonetheless, there are some in the political class who relish the sort of flying-elbow mayoral race that used to typify elections here, which often pitted candidates of the same ethnicity against one another, stripping away the danger of being perceived as racially antagonistic.
Before Menino took the mayoralty in 1993, the last non-Irish-American mayor of Boston was Malcolm Nichols, a former journalist who sandwiched a Republican mayoralty during the 1920s between a pair of James Michael Curley's terms.
Connolly is the scion of a well-connected political family, his father a former secretary of state, his mother the former chief justice of the state's district courts. Walsh is the son of Irish immigrants, his family steeped in the local labor movement.
With Tuesday's results, expect much chest-thumping about a restoration of the city's long-ruling Irish.
The November vote also echoes 1993, when Menino, from the same politically potent Southwest Corridor that helped boost Connolly on Tuesday, beat James T. Brett, then state representative, who lives in Walsh's Savin Hill neighborhood.
Like Menino and Brett, Connolly and Walsh come from the same generation. Most of their policy stances, too, are similar.
As in the preliminary, the state of the city's public schools will dominate much of the discourse, and the two-person choice in the final election will probably amplify their differences on that topic.
Connolly has made the teachers' unions livid, with his staunch support for lifting the cap on charter schools and lengthening the school day and the school year.
Those unions are less antagonistic toward Walsh, but still put off by his backing of education reform and charter schools, what labor movement strategists call one of the few blemishes in his otherwise prounion record.
Education policy sparked one of the most embittered moments of the preliminary, when an outside education advocacy group said it would commit more than $500,000 to back Connolly's campaign. Walsh, who received more outside spending assistance than the rest of the field combined during the preliminary, pounced, and Connolly quickly rejected the group's aid.
But outside spending will probably return in seven-figure totals during the six-week sprint to the final election.
For Connolly's policy agenda, the challenge will be to broaden beyond education reform, which he has fashioned into a signature issue. Walsh, who has portrayed himself as an avowed deliverer of human services, will need to blunt Connolly's claim on voters who prioritize public school improvement.
"John is laser-focused on education," Chang-Diaz said. "John is also working the new technology, new Boston brand, whereas what I've heard people say they like about Marty is he brings the best of a more traditional brand of politics, that very sort of person-to-person. He's helped so many people on a one-on-one basis."
Walsh and Connolly will now spend much of their time jockeying for their onetime rivals' backers. Among political insiders, political speculation had already begun by Tuesday over which loser might side with which finalist.
For Connolly, the city's electorally fertile southwest corner now has two vanquished sons, Councilor Rob Consalvo and Suffolk District Attorney Daniel F. Conley. Walsh's Dorchester neighborhood saw three prominent candidates fall away: Barros, Golar Richie, and former nonprofit health care executive Bill Walczak.
Still, there are numerous areas of the city — from Charlestown to Allston-Brighton, through the South End and South Boston, south through Roxbury to Mattapan — where the two finalists will scavenge for unaffiliated voters in the next six weeks.
According to Connolly's campaign data, Walsh beat Connolly 75 percent to 25 percent in his South Boston and Dorchester strongholds, while Connolly, a citywide councilor, topped Walsh in the rest of Boston, 63 percent to 37 percent.
Tuesday's results also hasten Menino's movement toward the exits. Connolly, in particular, angered Menino loyalists earlier this year when he announced he would challenge Menino regardless of the incumbent's intentions. But Menino's relationship with Walsh has also been strained, at times explosive.
For a 20-year mayor whose term midwifed so much change in Boston, Tuesday night may have been among the most unwelcome.