Independent pollsters, though, disagree, predicting easy victories for the two front-runners.
The nationally known Booker has had huge leads in polls - around 40 points - over Pallone, U.S. Rep. Rush Holt, and Assembly Speaker Sheila Oliver.
Lonegan, who has twice run for governor but lost in GOP primaries, has had an even larger advantage over physician Alieta Eck, who has never run for public office before. A Quinnipiac Poll released last week gave Lonegan a 74-10 lead.
Even Senate Majority Leader Harry Reid (D., Nev.) has openly predicted that Booker will join the chamber after October's special general election.
What remains unclear is how many voters will actually show up Tuesday and which ones.
"We really don't have any clue about what an August primary should look like," said Patrick Murray, director of the Monmouth University Polling Institute.
Asked Thursday how he planned to overcome Booker's lead in the polls, Holt questioned those surveys.
"Any prognosticator, any pundit, any pollster who says, 'I understand how this one-of-a-kind primary is going to work,' should be regarded with skepticism at least, if not disbelief," he said.
Oliver spokesman Michael Makarski said: "It's all about turnout. It's all about which candidate is going to be able to bring their base to the polls."
But Booker is so well-known that he leads whether polls sample a broad swath of voters or only the most active cohort, Murray said.
"We could have cut this at the die-hard primary voters. We could have cut it at the widest turnout you could expect," he said, "and it didn't change the dynamic."
His poll, too, gave Booker a massive lead.
While Booker faces established opponents - two veteran congressmen and one of the top two elected Democrats in the state - the short campaign gave them little time to introduce themselves to voters and chip away at Booker's popularity.
The campaign, originally expected to play out in 2014, suddenly began in June after the death of Sen. Frank Lautenberg. Booker already had a campaign up and running.
Pallone, Holt, and Oliver had to scramble.
They have spent most of the race trying to establish their identities with online ads while Booker touted his message on television.
"All campaigns had about 1,000 things to do or more instantaneously, and they all had to be done yesterday," said Ben Dworkin, director of Rider University's Rebovich Institute for New Jersey Politics.
"Booker was able to be at the next level from day one because he was already well-known. That's what helped him more than anything else."
Only in the past week have the congressmen stepped up their attacks on Booker, questioning his dedication to liberal causes, his record in Newark, and his ties to Wall Street and Republican Gov. Christie.
Booker took a verbal beating from Pallone and Holt in a Democratic debate Thursday, and a New York Times story raised questions about his ties to tech moguls who helped fund a start-up in which Booker has a valuable ownership stake - worth between $1 million and $5 million to the mayor.
Lonegan was on the defensive Friday over a racially charged (and quickly deleted) tweet his campaign aimed at Booker and Newark.
Eck said it showed that he is "completely unviable" as a candidate, though Lonegan's camp said the tweet was from a staffer and did not reflect Lonegan's views.
Those twists, though, have been the exception. They arrived so late that they may be a bigger factor in the general election than on Tuesday.
It takes time, Murray said, to "build a case" against a popular public official, and Holt and Pallone have not had time.
Booker's overall approval ratings, meanwhile, will help with the strange day at the polls. His team can pull wide swaths of voters, particularly from cities, knowing that the vast majority will pull the lever for him, even if a few also go for his opponents.
Pallone, Holt, and Oliver have a more delicate task. They'll have to more precisely target voters who they know will support them, and not one of the other candidates.
None of the Democrats has been tested statewide; they'll all have to reach beyond their home turf. But Booker is already known in many corners of the state, unlike his opponents.
"Booker's name recognition - it just swamps everything else," Murray said.
On the Republican side, Lonegan shares the same advantage Booker holds in the Democratic field: name identification.
"That is, in and of itself, going to help propel him to victory," Dworkin said.
Eck's campaign echoed Pallone and Holt. "In a low-turnout, low-information special election like this, absolutely anything can happen," said Thomas Roberts, Eck's campaign manager.
So far, though, not much has slowed the favorites. The rest of the field has two days to change that.
Contact Jonathan Tamari at firstname.lastname@example.org or follow on Twitter @JonathanTamari. Read his blog "Capitol Inq" at www.inquirer.com/CapitolInq.