ST. PAUL — When Rebecca Otto scored her first political win, few Democrats reveled in it more than Matt Entenza.

That was 2003, when Otto snatched a Republican-held legislative seat in a special election with the help of a Democratic House caucus led by Entenza. Back then he proclaimed Otto’s win “a political earthquake.”

A decade later, Entenza is seeking a new tremor by knocking off now-State Auditor Otto in a primary that has turned acrimonious and expensive. He’s spending loads of personal money — $675,000 as of Friday — and is driving hard at Otto on some issues barely connected to the office. As Otto defends her two-term record of government oversight, she’s also working to quell discontent in the Democratic stronghold of northeastern Minnesota over her position on exploratory drilling that some saw as anti-mining.

The matchup between the former Macalester College classmates and legislative colleagues developed when Entenza entered the race in the last hour of the last day of candidate filing. Tuesday’s winner moves on to a fall race against Republican Randy Gilbert, the Independence Party’s Patrick Dean and the Grassroots Party’s Judith Schwartzbacker.

Entenza has been out of elective office since he made an ill-fated run for attorney general in 2006. He took a shot at the governor’s office four years later, but finished third in a party primary despite spending millions from a family fortune. Entenza said his past as a white-collar crime prosecutor and his reputation as a watchdog of charter school finances put the auditor’s position right in his wheelhouse.

“I think I’m much better-suited to go after financial fraud and take a really deep look at spending that you want in an auditor,” Entenza said. “I’ve actually put people in jail for financial fraud.”

In television commercials — seldom aired in Minnesota auditor campaigns — he said he’d work to protect pensions (the auditor sits on the State Board of Investment) and “do more than just balance the books.” He has the backing of U.S. Rep. Keith Ellison and other lawmakers he’s worked with over the years.

Otto is also airing TV ads in which she says it’s “not a glamorous job” but one where keeping tabs on government spending is the core mission. She highlights her role as president of a national auditor’s association as a sign of her devotion to the post.

“I know the job, I love the job and I would love to do the job for another term,” she said in an interview this week.

At state Democratic Party headquarters, waves of mail pieces supporting Otto have gone out to Democrats and volunteers are logging more than 250,000 get-out-the-vote calls on behalf of her and other endorsed candidates in the final week.

But Entenza also bombarded potential primary voters with mailings. Some question Otto’s commitment to core party values based on votes she took long ago as a legislator on measures to impose new polling place restrictions and to bar gay marriage. He says the votes are fair game because they highlight an official’s decision-making.

“When you are auditor you have to make hard calls,” Entenza said. “People need to know you are willing to make hard calls even when it may be unpopular.”

Otto argues that Entenza is misconstruing her voter-identification position. And she calls the gay marriage vote her biggest mistake, one she atoned for by campaigning to defeat a same-sex marriage proposition on the 2012 ballot. In any case, she questions the relevance of those votes in the current contest.

“If you want to serve in a position you should understand that position and then talk about what you would do in that position,” she said. “As a state auditor, you audit. You provide oversight. That’s the job. He’s talking about everything but the job.”

She accuses Entenza of wanting the post as a steppingstone to higher office, which he denies. It has launched other politicians to bigger things: Gov. Mark Dayton was auditor first. So was former GOP Gov. Arne Carlson. The two auditors before Otto, Judi Dutcher and Patricia Anderson, tried unsuccessfully to trade up to governor.

The race could hinge on a vote Otto took last fall as a member of the state Executive Council to oppose exploratory drilling for copper-nickel mineral deposits. She was the only dissenting vote after expressing concern over the risks and whether there were adequate assurances that the industry would pay the cost of any environmental cleanup.

Entenza said he would have voted with Dayton and other state officers to allow the drilling to go forward.

Otto has worked to confront criticism that she risked impeding economic development in a region that sorely needs it. She still has the endorsement of the United Steelworkers Union, which has 12,000 members in the state.

“She’s explained herself on that vote and our members had no other reasons to believe different,” said Emil Ramirez, director of the union’s district that covers Minnesota and eight other states. “There are probably still people who have some concerns but we think the majority of steelworkers in the state are comfortable with her position.”