(CNN) - The battle for President Barack Obama's old Senate seat remains a deat heat, according to a new poll. A CNN/Time/Opinion Research Corporation survey released Wednesday also indicates the Illinois gubernatorial battle is all tied up.
Forty-three percent of likely voters questioned in the poll say they back Illinois Treasurer Alexi Giannoulias, the Democrat's Senate nominee, while 42 percent support Rep. Mark Kirk, the Republican standard-bearer.
Eight percent back Green Party candidate LeAlan Jones, while another four percent remain undecided.
Other polls of likely voters conducted this month also indicate the race is a dead heat.
"The key to this race may be Jones, whose support among liberals and independents is in double digits. Since 13 percent of the independents are currently opting for Jones, Kirk has a 16-point lead among that group," CNN Polling Director Keating Holland said.
"The race is also turning into a classic battle between Chicago and the suburbs, with Giannoulias holding a 23-point lead in Cook County and Kirk piling up a 25-point lead in the rest of Chicagoland."
Among the wider sampling of registered voters, the CNN/Time survey indicates that Giannoulias holds a six-point advantage over Kirk, suggesting a slight edge for the GOP when it comes to voter enthusiasm.
Giannoulias has seen his Senate bid rocked by controversy over his family's bank, which was taken over by federal regulators earlier this year. But Kirk, an intelligence officer in the naval reserve, has had his own problems this year, having to apologize for mischaracterizing portions of his 21-year military record, as well as being counseled by the military for violating rules that bar members of the armed services from partisan political activities.
The winner in November will succeed Democrat Roland Burris, who is not seeking a full term. Burris was named by now-ousted Illinois Gov. Rod Blagojevich to replace Obama, who stepped down from the seat following his victory in the 2008 presidential election.
In the gubernatorial contest, the poll indicates that 40 percent of likely voters back state senator Bill Brady, the GOP nominee, with 38 percent backing Gov. Pat Quinn, the Democrat's nominee.
Fourteen percent support independent Scott Lee Cohen, while four percent support Green Party candidate Rich Whitney.
"This is one of the first polls that has included Cohen's name in the list of choices offered to the respondent, and his double-digit support makes him the wild card in this race," Holland said.
"Illinois voters may be casting about for alternatives to the choices the two-party system has offered up, and the fact that Cohen is running as an independent may be attracting some voters. Add in the Green Party candidate and nearly one in five voters are currently opting for a candidate without a 'D' or 'R' after his name."
Quinn became governor last year, after Blagojevich was impeached and removed from office.
The CNN/Time/Opinion Research Corporation poll was conducted September 24-28, with 1,504 adults, including 1,360 registered voters in Illinois and 828 likely voters, questioned by telephone.
The survey's sampling error is plus or minus 2.5 percentage points for registered voters and plus or minus 3.5 percentage points for likely voters.
– CNN Deputy Political Director Paul Steinhauser contributed to this report