Bill Smith is "well positioned" to win the mayoral race in Monday's municipal election, according to the latest poll from Mainstreet Research, which puts him 13 points ahead of incumbent Naheed Nenshi among decided and leaning voters.

Among all voters, Smith's lead is a bit smaller, standing at 11 points.

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"What was once thought to be a sleepy election for Naheed Nenshi has turned into a nightmare," Quito Maggi, the polling firm's president, said in a release.

The poll, conducted for the company that owns the Calgary Sun and Calgary Herald, suggests Smith's lead has shrunk slightly compared to the last time the same company surveyed Calgarians a week ago.

"This is one of the most vicious and negative campaigns I have ever witnessed. Front-runner Bill Smith and incumbent Nenshi campaigns have both been plagued by self-inflicted wounds in the closing weeks," Maggi said.

"Most recently we have seen a series of stories hitting Bill Smith including coverage of e-mails, warrants and legal disputes."

Mainstreet's poll, the last before the election, found preference among leaning and decided voters to be:

Bill Smith — 52 per cent.

Naheed Nenshi — 39 per cent.

Andre Chabot — six per cent.

Someone else — three per cent.

Among all voters, Smith leads Nenshi by a margin of 47 per cent to 36 per cent.

The survey also asked respondents why they support a particular candidate.

Among Nenshi supporters, 22 per cent cited the way he represents Calgary at the provincial, national and international level, 18 per cent said he's the best option available, 15 per cent cited the city's financial performance under his leadership as mayor and nine per cent indicated his position on the arena deal with the Flames.

Among Smith supporters, 27 per cent cited his promise to hold the line on taxes while 22 per cent said he was the best option among the candidates and 17 per cent said his values reflect their own. Five per cent cited the arena deal.

"Finally, we asked Calgarians if they approved or disapproved of the performance by the candidates in the campaign. Forty per cent said they approved of Nenshi's performance while 48 per cent said they disapproved," Maggi said.

"When it came to Smith, 53 per cent approved of his performance and 29 per cent disapproved of it."

Mainstreet surveyed 1,500 Calgarians using automated, interactive voice-response (IVR) technology on Oct. 10 and 11 and responses were weighted using demographic and geographic information to targets based on the 2016 Census.

For comparison purposes only, a random sample of this size would yield a margin of error of plus or minus 2.5 percentage points, 19 times out of 20.

A survey using a different methodology and released earlier in the week by lobby group LRT On The Green, which asked respondents questions that mainly focused on the Green Line transit project but also about their mayoral preference, found 41 per cent preferred Nenshi compared to 26 per cent for Smith and 28 per cent undecided.