The future makeup of Houston City Council will largely be decided next month, following a Tuesday election in which all but four candidates failed to win a majority of votes in their respective races.

Among those who are now headed to a December runoff are incumbent, at-large candidates Mike Knox, David Robinson, Michael Kubosh, as well as District H Councilwoman Karla Cisneros, according to unofficial results.

Incumbents Dave Martin, Martha Castex-Tatum, Greg Travis and Robert Gallegos each easily won re-election. They were the only candidates to win outright, meaning that 12 spots on the body are still up for grabs.

All told, there were more than 100 candidates vying for council’s 16 spots, including eight incumbents. Council members are limited to two four-year terms, and this year half of the body retired or stepped down to pursue other offices.

Political experts had expected many incumbents to cruise to victory, but also said that they were monitoring the array of younger candidates to see how much they could mobilize millennial voters in this cycle.

Mark Jones, a political science professor at Rice University, noted that the challengers to Kubosh and Knox could mount particularly strong showings.

Knox had initially enjoyed a double-digit lead over his main challenger, former teacher and education nonprofit leader Raj Salhotra; and Kubosh’s majority share of votes steadily slipped overnight, meaning he’ll face Janaeya Carmouche in a runoff.

Robinson, meanwhile, will face Willie R. Davis in a repeat of a 2015 runoff in which Robinson prevailed by 10 points.

In the race for council’s fourth at-large position, Anthony Dolcefino, a millennial who has run on ethics reform, will face local business owner and doctor Letitia Plummer. The winner will replace Amanda Edwards, who announced in July that she is running for U.S. Senate.

Sallie Alcorn, a longtime City Hall staffer, will face Harris County Department of Education representative Eric Dick for the fifth at-large council race.

In District A, Amy Peck amassed the largest vote share of any non-incumbent, but fell just shy of a majority that’d avoid a runoff. Peck is Stardig’s current chief of staff, and her campaign has focused in part on the experience that position has given her. She’ll face George Harry Zoes, who came in a distant second place.

In District B, local organizer Tarsha Jackson led all candidates in the race to replace current Vice Mayor Pro-Tem Jerry Davis. She’ll now go head-to-head with community activist Cynthia Bailey.

In District C, civil rights attorney Abbie Kamin led 12 other candidates by double-digits, but will go to a runoff against Shelley Kennedy.

Carolyn Evans-Shabazz won a plurality of votes in a crowded, 15-candidate field for District D. She’ll face off against Brad “Scarface” Jordan, a former member of the Geto Boys hip hop group. The winner will replace Councilman Dwight Boykins, who lost his bid for mayor Tuesday.

In District F, Tiffany Thomas, a former trustee of the Alief Independent School Board, had a double-digit lead over all others in the six-candidate field. She’ll face Van Huynh in a runoff.

In District H, incumbent Karla Cisneros also had a double-digit lead over her four challengers, though she did not have a majority of votes. Cisneros won her first term by about 10 points during a 2015 runoff, and political experts have said she may face the toughest challenge of any incumbent in this year’s election cycle. She’s now headed to a runoff against Isabel Longoria, a a longtime public advocate who also serves on the City of Houston’s Planning Commission.

In District J, there was an almost dead-even tie between Edward Pollard, a nonprofit leader and former legislative aide, and Sandra Rodriguez, a Gulfton native who works in the city Health Department’s Bureau of Youth and Adolescent Health.

robert.downen@chron.com