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ABC's Michael Falcone and Shushannah Walshe report:

Cory Booker's got company.

The Newark mayor may be the early favorite in the fast-paced race to fill the U.S. Senate seat once held by the late Sen. Frank Lautenberg, but he will have to fend off challenges from several other Democrats and, eventually, a Republican general election opponent, before he can book a ticket to Washington.

Three other Democrats filed paperwork on Monday to run in the Aug. 13 primary:

• Rep. Frank Pallone, D-N.J.: Pallone, 61, represents New Jersey's 6th Congressional district and has been in office since 1989. He boasts an impressive campaign war chest of $3.7 million, which likely makes him Booker's stiffest competition. "I'm running for the Senate because we need to focus on getting people back to work, rebuilding our economy, making sure our environment is clean and safe for future generations, and standing up for equality for all Americans," Pallone said in a statement on Monday.

• Rep. Rush Holt, D-N.J.: Holt, 63, represents the state's 12th Congressional district and has held office since 1999. "I believe I am the best candidate to continue the passionate advocacy for progressive values that Sen. Lautenberg exemplified," he said in a statement announcing his candidacy. Holt is a former college physics professor.

• State Assembly Speaker Sheila Oliver: Oliver, who has served in the state legislature for more than a decade, would become New Jersey's first female senator if elected. When asked on Monday what she brings to the Senate contest, Oliver reportedly said: "I don't bring a sense of entitlement."

Candidates were required to submit papers along with 1,000 signatures to the New Jersey Division of Elections by 4 p.m. on Monday.

At least two Republican candidates filed papers to run in the GOP primary. The best-known is conservative activist Steve Lonegan, who ran unsuccessfully in the GOP gubernatorial primaries in 2005 and 2009. Lonegan served as mayor of Bogota, N.J. from 1995-2007, and he will likely face Somerset, N.J. physician Alieta Eck in the Senate primary.

Last week Gov. Chris Christie appointed Republican state Attorney General Jeff Chiesa to temporarily fill Lautenberg's seat. Chiesa, who was officially sworn in Monday afternoon, will only serve until the special election and did not file paperwork to run.

A Quinnipiac University poll out on Monday showed Booker trouncing all challengers in the Democratic primary field. In the survey, Booker got 53 percent of the Democratic primary vote, with 10 percent support for Holt and 9 percent for Pallone. (State Assembly Speaker Oliver was not included in the poll).

And, if Booker prevails in the primary, he would be the heavy favorite to win the Oct. 16 general election.

The same poll found Booker topping Lonegan 54 to 27 percent in a head-to-head match up. (Either of the two Democratic congressmen would likely face a closer race against Lonegan: Pallone leads the GOP candidate 39 to 29 percent and Holt leads 36 to 31 percent). New Jersey voters, by a 57 percent to 14 percent margin, also say they have a favorable opinion of the Newark mayor, who would have to run again in 2014 even if he wins this fall's special election.

"The record shows that Congressmen Frank Pallone and Rush Holt are big in their districts, but, state-wide, no one knows them," Maurice Carroll, director of the Quinnipiac University Polling Institute, said.

Another wildcard in the compressed special election contest is turnout. Brigid Harrison, professor of political science at Montclair State University, pointed out that there is no precedent for an August primary in the Garden State.

"It really will be who has the better organizational structure and it isn't always experience or even voters' positive perceptions of a candidate that are necessarily as important as a candidate's ability to turn out his or her supporters," Harrison said in an interview with ABC News.

Harrison acknowledged that Booker "clearly has an upper hand" when it comes to name recognition.

"He is well known, he has high positive perception…he's known throughout the country," she explained. "Compare that to any other Democrat even the congressmen Holt and Pallone. They are well known in their congressional districts, but less well known outside of their districts. What that means is there will be an extraordinary amount of money spent to increase name recognition to be on an even keel with Booker."

But, Harrison said "particularly Pallone" does have a shot because of the millions in campaign funds he has in the bank. "He certainly has a chance, but at this point I would say it's Booker's to lose," she added.