IT’S AS IF someone swapped out the “Vote Here” placards marking city polling places and replaced them with street signs common to the confusing tangle of Boston byways: “Left turn only.”

A city where municipal races were dominated 25 years ago by voters in the “high-numbered wards,” shorthand for the more conservative white residents populating perimeter neighborhoods like Hyde Park, West Roxbury, and coastal Dorchester, has been moving steadily away from that once predictable pattern.

Yesterday’s election put a fork in it.

Michelle Wu, an Asian-American Chicago native, ran away with the top spot in the at-large City Council race, a showing that will further fuel speculation about a challenge in two years to Mayor Marty Walsh. Two Latinas were separated by only 10 votes in the race for the fourth at-large council seat. The liberal contender prevailed in all three competitive district council races, with candidates supported by local political mainstays in Hyde Park and Allston-Brighton swept away by progressive and minority voters flexing their electoral muscle.

Regardless of the outcome of an expected recount involving Julia Mejia, who had a 10-vote lead over Alejandra St. Guillen in the at-large race, the 13-member council will have 8 women, its first female Latino councilor, and 7 people of color.

It’s a long way from the days of the Dapper O’Neil, the race-baiting throwback who was sent packing 20 years ago. His tired shtick was ended by then-newcomer Michael Flaherty, who fashioned himself as a new Boston candidate from an old-line South Boston family. Two decades later, Flaherty looks very much like the old guard, and his third-place at-large finish made him an anomaly amidst the lefty wave washing over city politics.

City election outcomes have often lagged the broader transformations occurring in Boston. “But for the first time in memory, the City Council is a barometer of a city that is changing — one in which progressives now routinely beat moderates,” writes the Globe’s Adrian Walker.

“The council has been quietly transforming itself for six years, from a small-bore, pothole- obsessed group of neighborhood operators into one with grander ideas about its place, one that thinks of itself as a branch of government — even if not a coequal one,” he adds.

As it thinks about those bigger ideas, the council agenda will be very much shaped by the changing make-up of its membership.

“Think about the folks who are going to have voices now,” Ricardo Arroyo, a Latino lawyer and son and brother of former city councilors, said at his victory party in the race for the open District 5 seat in Hyde Park. “Think about the issues that are going to be lifted up.”

As David Bernstein points out, the inroads made in recent years by minority candidates and others traditionally not part of the city’s power structure have come from those who had one foot firmly in the political structure, while championing “outsider” issues that appeal to progressive voters.

Arroyo certainly represents that. Bernstein also cites, among other examples, Wu’s background working for Elizabeth Warren and Tom Menino and City Council President Andrea Campbell’s prior stint in state government under Deval Patrick. He suggests the winning recipe is one that finds a middle ground between the revolution and business as usual.

“Boston voters aren’t looking for bomb-throwers and rabble-rousers, but neither are they seeking go-along friends of the powerful,” Bernstein writes for WGBH.

Walsh still stands as the undisputed heavyweight of city politics. At least for now.

It’s been 70 years since anyone ousted an incumbent Boston mayor. But few saw Ayanna Pressley’s huge victory coming in her race last year against a 20-year congressional incumbent. Time-honored certainties in politics seem less certain these days. At a minimum, Walsh will have to contend with a City Council that’s unlikely to be the pushover of the past.

“Taken together,” writes Walker, “the results point to a council that could be a potent counterweight to the nearly unchallenged influence of the mayor.”