A new poll taken over the weekend — just after Seattle Councilman Tim Burgess made his surprising departure from the race — shows Mayor Mike McGinn clinging to a narrow lead over ex-councilman and architect Peter Steinbrueck.

That’s right, Steinbrueck, long considered the dark horse in the field, is picking up traction. The son of the man who saved Pike Place Market is making a strong case that he is a viable contender in the battle to become Seattle’s next mayor.

According to a KING 5 News poll, McGinn leads with 22 percent, followed by Steinbrueck with 17 percent. State Sen. Ed Murray finished third with 15 percent and Councilman Bruce Harrell had 12 percent..

“I’m elated,” Steinbrueck told Seattle Weekly. “I think this puts me within striking distance.”

Steinbrueck attributed his strong showing to the fact that people are beginning to pay closer attention to the race, and “I think I have a strong and enduring base of support in Seattle.”

Still, the race remains volatile, with nearly a quarter of the electorate undecided about how they plan to vote for in the August 6 primary.

SurveyUSA asked 552 registered voters over the weekend who they would vote for if the election were held today. The margin of error is plus or minus 4.3 percent.

Kate Martin and Charlie Staadecker have 4 percent and Mary Martin has 3 percent.

In a similar poll in March, McGinn was tied with former King County Executive Ron Sims for the lead with 15 percent, followed by Seattle City Councilmember Tim Burgess with 10 percent. But since then, Sims reportedly said he would not enter the race. Burgess announced last Friday he was dropping out.

The number of undecideds in the March poll was 34 percent.