Lonegan holds a slight lead among men, with 48 percent support to Booker's 46 percent, but the Newark Mayor has nearly twice as much female support as Lonegan, 60 percent to 34 percent.
Booker is still the heavy favorite to win the special election to replace the late Sen. Frank Lautenberg (D-N.J.), in a state as blue as New Jersey with just three weeks left till Election Day.
Though he nabbed the endorsements of both Sen. Rand Paul (R-Ky.) and New Jersey Gov. Chris Christie, Lonegan has failed to pick up much traction among conservatives in New Jersey or nationwide and has struggled to raise funds to support his bid.
But the poll, and a trend of declining support this month, seems to indicate increased scrutiny on Booker's former startup, his Wall Street and Hollywood ties and his home ownership in Newark may have taken a toll on his once sky-high support in the race.
A Rutgers-Eagleton poll conducted at the beginning of September gave Booker 64 percent to Lonegan's 29 percent support.
Quinnipiac University surveyed 948 likely voters from Sept. 19-22, and the poll has a margin of error of plus or minus 3.2 percentage points.