If Republican John Cox can hang on to finish second in the June 5 primary for governor, he’ll be doing it with a mighty short bankroll.

Campaign finance reports released Thursday show that Cox’s campaign is beyond broke, with $124,017 in the bank and $277,751 in unpaid bills.

The San Diego-area businessman plunked another $100,000 into his campaign Tuesday, bringing his personal contributions to $4.4 million.

“The Democrat billionaires are spending millions attacking us,” said Tim Rosales, Cox’s campaign manager. “John Cox is prepared to do whatever it takes to make the runoff and give voters a Republican choice in November.”

Recent polls show Cox clinging to the all-important second spot in the primary, with Democrat Antonio Villaraigosa close behind. Both trail Democratic Lt. Gov. Gavin Newsom, with the top two finishers advancing to the November election.

The new financial reports were more good news for Newsom, who raised more than any other candidate for governor between April 22 and May 19, the cutoff date for the latest numbers.

The former San Francisco mayor spent $9.6 million in that period and has about $12.7 million in the bank, including $2.9 million left from his 2014 re-election campaign.

Newsom has received more than 120,000 individual contributions, averaging under $200 each, his campaign said in a statement.

None of the other leading candidates for governor has anything like Newsom’s cash. State Treasurer John Chiang has $4.3 million in the bank, while Villaraigosa, former mayor of Los Angeles, has $2.2 million.

The campaigns for Democrat Delaine Eastin, former state schools chief, and Republican Assemblyman Travis Allen, are both running on fumes. Eastin reported $127,413 in the bank and $111,799 in debts, while Allen has $37,539 cash on hand and $17,866 in unpaid bills.

Chiang, looking to make up ground in the race, has been constantly attacking Newsom and Villaraigosa in the past couple of weeks. The finance reports gave the campaign another opportunity.

“John is proud of the grassroots army of activists that have come out to support and donate to our campaign,” Fabien Levy, a spokesman for Chiang, said in a statement. “Voters want to elect someone who will fight for them, not someone who has been bought and paid for by billionaires and special interests.”

Chiang raised $613,894 in the most recent period, compared with $969,477 for Villaraigosa and $1.5 million for Newsom.

Villaraigosa, however, has the support of an independent expenditure committee of wealthy charter school supporters that has raised more than $17 million to support his campaign and still has $1.7 million in the bank. That’s money that could make a difference in the final few days before the election.

A consultant for that Villaraigosa-friendly committee also had a unique take on Newsom’s finances, arguing that the front-runner’s heavy spending hasn’t translated into improving poll numbers.

“Gavin Newsom’s prospects in November seem weaker every day,” said Josh Pulliam, a consultant for Families and Teachers for Antonio 2018. “After dropping $15.5 million in this race, Newsom’s campaign has sunk 5 percent in the polls and the vast majority of Californians aren’t interested in what he’s selling.”

But even the internal tracking polls Pulliam is quoting put Newsom on top of the primary race at 26 percent earlier this week, with Cox at 19 percent and Villaraigosa at 16 percent. With the election a little more than a week away, that’s a big mountain to climb against a well-known candidate with all the money he needs.

John Wildermuth is a San Francisco Chronicle staff writer. Email: jwildermuth@sfchronicle.com Twitter: @jfwildermuth