State Senate candidate Gustavo Rivera has picked up significant support in his bid to topple incumbent Pedro Espada, Jr. in the 33rd Senate District. The Working Families Party and the New Roosevelt Initiative have gotten behind Rivera, and the latter promises to independently spend $250,000 on his behalf.

Meanwhile, Daniel Padernacht, a Kingsbridge Heights housing lawyer, and Fernando Tirado, the district manager of Community Board 7, are committed to staying in the race, despite pressure to withdraw so Rivera can take on Espada one-on-one in the Democratic primary on Sept. 14. (Desiree Pilgrim-Hunter withdrew from the race two weeks ago, citing a lack of money.)

Conventional political handicapping holds that multiple challengers will favor Espada in the primary. But Rivera, a longtime Democratic political operative who is stepping out from behind the scenes as a candidate for the first time, is gaining powerful backing.

The Working Families Party will supply pro-Rivera organizers and foot soldiers essential to energizing voters and getting them out to the polls, critical efforts in what usually is a low-turnout race.

Councilman Oliver Koppell endorsed Rivera in an announcement at Amalgamated Houses last week, and the Riverdale-based Benjamin Franklin Reform Democratic Club is also backing Rivera.

Padernacht said he received numerous calls asking him to step down in the days leading up to the July 19 deadline to remove candidates’ names from the ballot.

Specifically, Padernacht said he received pressure from SEIU 1199 (the healthcare workers union) and the office of Public Advocate Bill de Blasio. Neither SEIU or de Blasio’s office returned calls seeking comment.

Padernacht said he was not convinced by the primary argument made by those wanting him to withdraw, which is that he will take away votes needed to defeat Espada.

“I don’t agree with their numbers,” he said, adding that he believes there will be a higher turnout for this race than the last one in 2008 because there will be much more interest. That race pitted Espada against indicted incumbent Efrain Gonzalez, now serving a seven-year prison sentence for fraud. Espada won with a little less than 5,000 votes out of a total of 8,352.

Tirado, who was ordered to take a leave at Community Board 7 during his campaign, said Rivera asked him if he would step down in the interest of defeating Espada. Rivera also told him that he was officially challenging his petition signatures.

Tirado says he has more than 1,500 signatures, while Padernacht, who says he’s also being officially challenged by three different people, says he has around 4,500. Rivera says he has 6,200.

“I told [Rivera], ‘This is the democratic process and if you feel strongly about it [you should let it take its course],” Tirado said. If others called, he said he would tell them the same thing: he’s staying in the race.

Padernacht said it was a tough decision to stay in the race and that he did “a lot of soul searching” in the hours leading up to the deadline. But he said that calls for him to step down did not put much faith in voters’ ability to make up their minds. “If I accept their view, I’m accepting a cynical pessimistic view of our community.”

At the press conference with Koppell last week, Rivera, who most recently worked as an outreach coordinator for U.S. Senator Kirsten Gillibrand, brushed off concerns that a more crowded race would hurt his chances at victory. But he added that all the challengers could agree on one thing: Espada needed to go.

Local resident Kristin Hart, who attended the press conference, said the piling on of political endorsements for Rivera made her uneasy, like there was a backroom deal in place. “It feels like they’re telling the electorate it’s not intelligent enough to make its own decision,” she said. “They have no faith in the democratic process.”

After the press conference, Rivera went up to Hart and asked if he could address any concerns she had.

“I tell everyone I meet that I want to be accountable to [them],” Rivera said later. “The last thing I tell them is that I hope this is not the last conversation we have.”