Sources: Runner-up to Concede N.Y. Mayoral Primary

New York Democratic mayoral hopeful Bill Thompson speaks to his supporters after the polls closed, Tuesday, Sept. 10, 2013, in New York. Thompson will concede, sources say.
Associated Press + More

By JENNIFER PELTZ and JONATHAN LEMIRE, Associated Press

NEW YORK (AP) — New York City mayoral candidate Bill Thompson will concede the Democratic primary race to front-runner Bill de Blasio on Monday, averting a potential runoff, two people familiar with the decision said.

Thompson will drop out of the race and endorse de Blasio at an 11 a.m. event at City Hall, according to the people, who spoke on condition of anonymity ahead of the event where the announcement was to be made.

[READ: Bill de Blasio, Joe Lhota Win New York Mayoral Primaries]

The potential Oct. 1 runoff had loomed as another act in the Democratic drama over choosing a successor to three-term Mayor Michael Bloomberg — a drama that would keep Democrats tilting at each other while Republicans and independents looked ahead to the general election. With Thompson, the Democrats' 2009 mayoral nominee, out of the race, de Blasio would face Republican nominee Joe Lhota on Nov. 5.

Gov. Andrew Cuomo played a role in brokering the deal, according to the people. Cuomo was expected to attend the City Hall event, which has been billed as a "unification rally."

In unofficial returns with 99 percent of precincts reporting, de Blasio had had 40.3 percent of the vote — slightly more than the 40 percent threshold needed to win outright. Thompson was second with 26.2 percent.

A runoff had long been expected in the crowded Democratic race. But after last week's unofficial returns put de Blasio above the 40 percent mark, Thompson faced pressure to concede and spare the party further division ahead of the general election.

[READ: Bill de Blasio Rockets Toward NYC Democratic Mayoral Nomination]

He said as recently as Sunday he would wait until the official tally was finished.

"I think that's important. We want to see every vote counted," he said then.

The Thompson campaign did not respond to requests for comment Monday morning.

Thompson called the Rev. Al Sharpton, an important city power broker, to inform him early Monday of his decision, according to a person close to Sharpton who was not authorized to speak on his behalf and thus spoke on condition of anonymity.

Sharpton endorsed his longtime friend Thompson during his 2009 mayoral bid but stayed on the sidelines this race, depriving Thompson of a loud advocate in his bid to win the majority of African-American voters. De Blasio and Thompson ran even among African-American voters, according to exit polls.

Sharpton was not expected to attend the morning rally but will likely endorse de Blasio in the coming days, according to the person.

[READ: Anthony Weiner Slips in N.Y. Mayoral Race]

Currently the city's elected public advocate, de Blasio has been riding a wave of momentum that built during the last month of his campaign, which he billed as "a progressive alternative to the Bloomberg era."

After lagging in the polls, de Blasio got voters' attention by protesting a hospital closing — and getting arrested — and airing ads in which his teenage son gave voice to his liberal platform and showed New Yorkers de Blasio's interracial family.

Thompson, a former city comptroller and the only African-American in the race, has run a more centrist campaign, offering himself as a seasoned, thoughtful manager.

Thompson hadn't led in polls of the crowded Democratic field this year, but supporters noted that he had been underestimated in the past: Thompson came much closer than polls predicted to unseating Bloomberg in 2009, despite being vastly outspent.

De Blasio has said Thompson had every right to want the official count.

[OPINION: Michael Bloomberg, Bill de Blasio, Racism and 'Class Warfare' in New York's Mayor Race]

On Friday, elections officials began checking vote totals from more than 645,000 ballots cast via lever machines that were hauled out of storage for the primary, after the elections board worried it wouldn't be able to reprogram the city's newer, optical-scanner devices for a potential runoff. That count was finished Sunday night and was to be announced Monday afternoon.