Colorado Gov. John Hickenlooper’s race against Republican Bob Beauprez was too close to call in a new Denver Post poll in which voters nonetheless indicated they were still getting familiar with the challenger.

Five weeks before the start of the mail-in election, 45 percent supported Hickenlooper among likely voters polled by SurveyUSA, and 43 percent supported Beauprez. The result is within the margin of error of plus or minus 3.9 percentage points.

The poll makes clear that the Democratic governor — who has faced controversy over gun control, the death penalty and his unconventional leadership style — is mostly a known quantity, and a polarizing figure. Forty-six percent of respondents had a favorable opinion of him, while 47 percent had an unfavorable opinion, a one-point deficit.

“It’s a first-of-a-kind for John Hickenlooper, in that his charmed political life” has stalled out, said Eric Sondermann, a Denver-based independent political analyst. “Now all of the sudden, he has a real race on his hands.”

The poll’s Senate race results placed Democratic Sen. Mark Udall ahead of Republican Rep. Cory Gardner, 46 percent to 42 percent.

In the governor’s race, Beauprez’s favorability rating was 38 percent positive and 34 percent unfavorable.

But 28 percent said they needed to know more about Beauprez, a former congressman who ran unsuccessfully for governor in 2006, to form an opinion. Only 7 percent had no opinion about Hickenlooper.

Opinions among some of those surveyed were mixed.

“(Hickenlooper) doesn’t have a very strong backing from me, other than he’s done a pretty good job in creating jobs for Colorado,” said Chris Delaney, 29, a Denver resident who told SurveyUSA he planned to vote for the governor despite disapproving of his performance. “But that’s not the only thing a governor’s supposed to do. He just doesn’t seem to represent my views and things that are important to me.”

The registered Democrat considered Hickenlooper “an amazing mayor” of Denver. But now he sees him as too friendly to oil and gas companies and unable to decide on Chuck E. Cheese killer Nathan Dunlap’s execution.

Those same views were cited by another respondent, Keith Reagan, 77, of Colorado Springs, who also disliked Hickenlooper’s signing of gun control measures last year. He plans to vote for Beauprez.

“I don’t know much about Beauprez except he lost his last election,” said Reagan, a registered Republican. “And Hickenlooper, I just don’t like the way he does things.”

The pollsters noted that Hickenlooper led by 20 percentage points among moderates, and more narrowly by 4 percentage points among independent, or unaffiliated, voters. But 14 percent of that latter group supported third-party candidates in the poll.

“Where these disaffected independents go on Election Day may well determine the outcome,” the pollster’s analysis says.

The statewide survey of 664 likely voters, conducted Sept. 8 to 10, is the first of three planned by The Post before the Nov. 4 election. Clerks will send mail ballots to voters beginning Oct. 14.

That means the clock is ticking for Hickenlooper.

The results of The Post’s poll fit within the trend line for the race, with the RealClearPolitics polling average putting Hickenlooper up by a mere 0.6 percentage points. Two other polls released in the past week had tight results: Hickenlooper led 43 percent to 39 percent in an NBC News/Marist College poll; and Beauprez led 45 percent to 44 percent in a Rasmussen Reports poll.

The Post’s poll is the first survey conducted since Hickenlooper and Beauprez debated for the first time Saturday in Grand Junction.

Sondermann, the political analyst, says Beauprez likely will attract more donations as he looks more viable. And Hickenlooper, who has vowed not to run negative ads, may be stuck.

“The only way you bring down favorability ratios is with negative ads,” Sondermann said, though outside groups could ramp up attacks on Beauprez.

Hickenlooper’s campaign didn’t express worry about the tight poll result: “We have real momentum right now,” campaign manager Brad Komar said, adding that the campaign is focused on promoting the strong Colorado economy and Hickenlooper’s small business background.

Beauprez spokesman Allen Fuller said the campaign was encouraged by the poll but added: “The governor should be very concerned that three polls this week have shown him in the low- to mid-40s.”

The Post poll’s main question, asking whom respondents would support if the election were held today, also included three candidates beside the main contenders. Four percent supported Libertarian Matthew Hess; 2 percent supported unaffiliated candidate Mike Dunafon, the Glendale mayor; and 1 percent supported Green candidate Harry Hempy.

Five percent of respondents still were undecided on their vote for governor.

After a year in which Hickenlooper has faced intense scrutiny for delaying Dunlap’s execution, leaving the ultimate decision to the next governor, the poll found that capital punishment isn’t playing a dominant role in most voters’ decisions.

Sixty-three percent of respondents said they support the death penalty in Colorado, with 28 opposed and 10 percent unsure.

But only 18 percent said the issue was a major factor in their vote, with 47 percent saying it was a minor factor.

Other poll findings on the gubernatorial race:

• Hickenlooper can thank minority voters for his small lead, the pollster says, though Hispanics, a critical constituency, favored him barely, 46 percent to 44 percent, within the margin of error.

• Hickenlooper’s approval rating was 46 percent, with 45 percent disapproving of the job he’s doing as governor.

• Forty-two percent said Hickenlooper is more trustworthy, versus 38 percent putting more trust in Beauprez.

• Respondents were nearly split on who would make the best decisions in office: 42 percent said Hickenlooper and 41 percent said Beauprez.

The poll found Hickenlooper and Beauprez each enjoy similarly strong support exceeding 80 percent within their parties’ bases.

Jon Murray: 303-954-1405, jmurray@denverpost.com or twitter.com/JonMurray

Methodology

The Denver Post’s poll by SurveyUSA was conducted Sept. 8 through Sept. 10. Pollsters started with 850 Colorado adults and narrowed the field to 664 likely voters. SurveyUSA contacted both landlines and cell phones. The poll results have a margin of error of plus or minus 3.9 percentage points. Pollsters weighted the sample by gender, age, race and region, but not by party identification. The party affiliation breakdown of the sample, with numbers rounded, was 33 percent Republican, 33 percent Democratic and 33 percent unaffiliated.