(CNN) - Illinois state Rep. Robin Kelly, who was boosted by support from New York City Mayor Michael Bloomberg, won a primary election in Chicago Tuesday, putting her closer to filling the vacant seat previously held by disgraced former Rep. Jesse Jackson Jr.
Her chief rival, Democratic State lawmaker Debbie Halvorson, conceded the race shortly after 8 p.m. local time.
There were more than a dozen candidates vying for the Democratic nomination, where the winner needed a simple plurality. The district includes parts of Chicago's South Side and has long been dominated by Democrats, making Kelly the likely frontrunner in the April 9 general election.
Illinois' second congressional district was until recently represented by Democrat Jackson, who pleaded guilty in federal court last week to using campaign funds for personal use.
The election was the first congressional contest since December's mass shooting at Sandy Hook Elementary School in Newtown, Connecticut, which put gun control back into the national political spotlight. The district includes some areas hit hard by the increased gun violence in Chicago. Some 506 people were murdered in the city last year, according to local crime statistics, up from 433 in 2011. January already set a bloody record, with some 43 people killed.
Halvorson has an "A" rating from the National Rifle Association, and opposes an assault weapons ban. She was the target of negative ads from Independence USA, a political action committee supported by Bloomberg. In total, the group spent more than $2 million on the race.
Kelly, on the other hand, is a strong supporter of gun control efforts and received the backing of Bloomberg’s organization.
"This is an important victory for common sense leadership on gun violence, a problem that plagues the whole nation,” Bloomberg said in a statement Tuesday night. “And it's the latest sign that voters across the country are demanding change from their representatives in Washington - not business as usual.”
In her concession speech, Halvorson said she was ready to support Kelly in the general election, but that the overwhelming influence of outside groups like Bloomberg’s was unfortunate.
“There was $2.3 million dollars minimum spent against me,” she said. “Someone timed it. Every seven and a half minutes there was a commercial.”
“That’s the way it is. I can’t help it,” she added later.
Jessica Taylor, a senior analyst and reporter for the non-partisan Rothenberg Political Report, said there is “no question the New York City mayor's multi-million dollar investment has had an outsized impact in the race.”
"The Independence PAC has been carpet bombing the district with expensive broadcast TV ads boosting Kelly, and Kelly is the only candidate with enough money to go up on cable, also with an ad touting her record on gun control,” Taylor continued.
Halvorson is white, while Kelly is black. Another black candidate, state Sen. Toi Hutchinson, dropped out of the race two weeks before primary day, as she came under attack by the commercials from Bloomberg's PAC, but also amid concerns that she and Kelly would split the African American vote.
Gun control has long mattered in Chicago elections and the Sandy Hook shootings have put the issue back in the spotlight nationally. The big question is whether the controversial issue will continue to dominate as next year's midterm elections draw closer.
"While it's very easy for a special election to become an incubator for the national issue of the day, it is less clear the issue will resonate on a national scale in 2014," adds Taylor.
CNN's Kevin Liptak contributed to this report.
An earlier version of this story erroneously reported the number of murders in Chicago last year.