The Flaherty-Yoon marriage

Not so fast, folks.

Yesterday, challenger Michael Flaherty made the kind of big league move it will take to recast the campaign dynamic. Flaherty, who finished second in the preliminary election, announced he was forming a political partnership with Sam Yoon, who finished third.

In a formal sense, all that really happened is that Yoon endorsed Flaherty for mayor of Boston and said he’ll campaign for him, while Flaherty announced that if he wins, he’ll make Yoon his top adviser, with the nifty title of deputy mayor.

“Alls I can say is that the mayor has [chief aide] Mike Kineavy; I’m going to have Sam Yoon,’’ Flaherty said, in an apt encapsulation of what the partnership translates to in concrete terms.

What actual power will Yoon have - and what happens if, after a couple of years, Flaherty gets sick of his deputy mayor? I asked.

“Sam will obviously be helping me lead the city and helping me make decisions on behalf of all of the residents of our city,’’ was Flaherty’s somewhat nebulous response. Although he left my other query hanging, the answer is clear: Yoon would serve at Flaherty’s pleasure, as does any mayoral hire.

Politically, however, Flaherty’s reach-out was a bold - and potentially game-changing - gambit.

“This is something that I have never known to be done before and I have been following this stuff for about 50 years,’’ says Larry DiCara, our walking repository of Boston’s political history.

Until yesterday, the final election seemed destined to be yet another plodding affair of the sort we’ve seen since Menino became mayor back in 1993, a race where a distant challenger struggled to little avail to gain traction against a powerful, well-funded incumbent.

But by making Yoon his informal teammate, Flaherty has done several important things.

First, he’s given Yoon’s disappointed followers a concrete reason to support him over Menino - something that was far from a foregone conclusion. Although they share many of the same stands, Flaherty, a South Boston native with familial roots in Old Boston, and Yoon, a Dorchester transplant who is quintessential New Boston, are very different culturally. Now, with Yoon on board as an endorser who has been promised a leading role in a possible future Flaherty administration, consolidating the votes of those tired of Menino should become significantly easier.

Next, Flaherty has injected some substance into his assertion that city government shouldn’t be all about one person. Heretofore, that sounded like the predictable rhetoric of an underdog challenging an entrenched incumbent. But by forging a political partnership with Yoon, Flaherty has demonstrated that he is willing to share the spotlight and perhaps even some power. Further, Flaherty pledged that he himself would not serve more than two terms if elected mayor, and he told me later that he would also push for a mayoral-term-limits measure, one of Yoon’s signature issues.

Third, this pairing offers something greater than the sum of its political parts. Separately, neither Flaherty nor Yoon was particularly convincing. Although smart and idealistic, Yoon leans toward a process-preoccupied wonkiness, which led to doubts about whether he was tough or cagey enough to run a city like Boston.

There’s little doubt that Flaherty, the erstwhile City Council president, has the requisite toughness. However, as the son of a former South Boston state representative and a candidate with ties to Southie’s old-school political network, he has had trouble establishing himself as a credible change agent.

But by marrying Flaherty’s political savvy with Yoon’s good-government reform impulse, this informal team becomes more convincing than either candidate was or would be by himself.

Finally, the alliance of Flaherty, 40, and Yoon, 39, against the 66-year-old Menino could also cast the race in distinct generational terms.

That’s why this is an impressive play, one with the potential to create an exciting, and competitive, mayoral final.

Or, as a fired-up Flaherty put it yesterday as he stood with his new teammate on City Hall Plaza: “There’s a real race for mayor, folks, in Boston. It starts today.’’

Scot Lehigh can be reached at lehigh@globe.com.