O'Connor won nearly 48 percent of the vote, while Napolitano won 42 percent. Business owner Joe Lomanto won 9 percent, officials said. Since no candidate won more than 50 percent, a runoff will be held.
Napolitano, who lives in Edison Park with his wife and three children, said his campaign was boosted by anger about the hundreds of flights every day over parts of Norwood Park, Edison Park and Edgebrook, where residents heard very little jet noise until a new east-west runway opened in 2013.
"That is a huge issue," said Napolitano, who served as a police officer before joining the fire department. "We can't just throw our hands up."
Many residents of the 41st Ward are firefighters, police officers and city workers.
O'Connor declined Tuesday night to discuss the results of the election, which she had been expected to win outright.
O'Connor, a frequent supporter of Mayor Rahm Emanuel, campaigned on her record in office, saying $100 million had been invested in the ward's schools during her tenure, including three new elementary school annexes and a $17 million renovation project at Taft High School.
Votes from two precincts in the 41st Ward are outstanding and will be counted later after hours at one polling place had to be extended an hour to compensate for a late start.
Napolitano, who touted his endorsement by the Chicago Republican Party in the last days of the campaign, said he would focus on making the ward office more responsive and transparent, while improving city services.
O'Connor had a significant financial advantage over her two opponents in the campaign that ended Tuesday.
"We got this far on a shoestring," Napolitano said. "And now we're in a spot no one expected."
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