ALBANY - Progressive activists successfully wrested the Democratic nominations away from six former members of the Senate Independent Democratic Conference in primaries on Thursday, including the conference's former leader, Jeff Klein.

Klein was trailing challenger Alessandra Biaggi by more than 6 percentage points, but with less than 10 percent of precincts left as Biaggi was declared the unofficial victor.

The outcome marked a stunning epilogue to the rogue group formed by Klein in 2011, after Democrats lost the chamber, and the initial four members worked, with the tepid support of Gov. Andrew M. Cuomo, in conjunction with the Senate Republicans. In 2013, when Democrats made up a numerical majority, the renegade Democrats enabled Republicans to maintain control of the Senate.

All eight of the former IDC members faced ardent primary challenges from their left flank, despite rejoining the mainline Democratic Conference in April as part of an effort to placate their critics and avoid challenges.

But their allegiance with Senate Republicans had fueled controversy about Albany's dysfunction and back-room dealing for years, and arguably set the stage for their startling defeats in Thursday's primary.

In a rematch of a multi-field race from 2016, former New York City Councilman Robert Jackson easily defeated freshman Sen. Marisol Alcantara in Manhattan.

In Brooklyn, two-term incumbent Jesse Hamilton fell to political newcomer Zellnor Myrie.

In Queens, Sen. Jose Peralta lost to Jessica Ramos.

In central New York, incumbent David Valesky trailed Rachel May by 3 percentage points, with less than 7 percent of precincts reporting.

Queens Sen. Tony Avella lost to John Liu, who, if elected in November, will be the only Asian-American member of the chamber.

Senators Diane Savino and David Carlucci cruised to renomination.

Sen. Marty Dilan, an ally of the former IDC members, lost overwhelmingly to first-time candidate Julia Salazar.

Aside from the seat in central New York, the other seats held by the former IDC members are expected to easily remain in Democratic hands in 2019.

Sen. Simcha Felder, a Brooklyn Democrat who caucuses with the Senate Republicans, was also poised to win the Democratic primary.

Senate Democratic Conference Leader Andrea Stewart-Cousins, who backed Klein, said in a statement on Thursday night that the results made it clear that "politics as usual are no longer acceptable."

The hopes of the challengers, like Biaggi, were buoyed by the upset primary win in June by Democrat Alexandria Ocasio-Cortez, who unseated U.S. Rep. Joe Crowley. But most political observers didn't expect three-quarters of the former IDC members to lose their nomination fights.

In April, the now-eight members of the IDC rejoined the Democratic Conference in a deal brokered by Cuomo, which included a promise that the party establishment would refrain from supporting primaries against the incumbents.

The agreement did little to quell criticisms of the eight senators from the liberal wing of the party and progressive activists. The Working Families Party, which tried to negotiate a deal in 2014 with Cuomo to bring the IDC back into the fold, continued to back challenges after the deal was reached.

The incumbents were backed by independent campaigns from the charter school and hospital industries, which spent hundreds of thousands of dollars on advertisements. They also benefited from a special campaign fundraising agreement with the Independence Party, which transferred more than $1 million into their coffers this year.

Klein was expected to spend about $2 million on his primary this year.

In January, a former legislative staff member accused Klein of forcibly kissing her three years ago outside an Albany bar. He vehemently denied the allegations and requested an independent investigation into the matter, but no findings have been issued.

David.Lombardo@timesunion.com - 518.454.5427 - @poozer87