Perhaps more than any other franchises, the Pittsburgh Steelers and the Chicago Bears have been defined by defense.

One week into this season, they're each scrambling to persevere without their current defensive cornerstone.

Injuries will keep Pittsburgh's Troy Polamalu and Chicago's Brian Urlacher off the field Sunday afternoon at Soldier Field, where the Super Bowl champion Steelers will try to build on an overtime win as they face a Bears team hoping to forget a turnover-plagued debut from quarterback Jay Cutler.

Joe Greene, Jack Lambert, Jack Ham and Mel Blount were the stars of a Pittsburgh defense that helped lead the franchise to four Super Bowls in the 1970s, while Dan Hampton and Mike Singletary led the 1985 Bears' championship unit that was arguably the most dominant defense in NFL history.

All six of those players have been enshrined in the Pro Football Hall of Fame, an honor Polamalu and Urlacher may one day receive.

For now, though, they'll have to settle for watching their teammates in street clothes. Polamalu tore the medial collateral ligament in his left knee as the Steelers kicked off the NFL season with a 13-10 win over Tennessee on Sept. 10, while Urlacher dislocated his wrist last Sunday in Chicago's 21-15 loss at Green Bay.

Urlacher -- a six-time Pro Bowler -- is out for the season, while Polamalu, who's been to five Pro Bowls, will miss at least three to six weeks.

"Injuries are a part of football," Steelers coach Mike Tomlin said. "I'm sure they'd prefer to play with Urlacher. They're going to have to find ways to be successful without him; similarly, we'd prefer to play with Troy. ... That's the story of the National Football League."

Hunter Hillenmeyer will fill the void for Chicago at middle linebacker, and the seven-year veteran isn't without experience playing alongside -- and in place of -- Urlacher. Hillenmeyer has made 49 starts at outside linebacker for the Bears, and also played seven games in the middle in 2004, while Urlacher was injured.

"Especially from an assignment standpoint, I feel very comfortable," Hillenmeyer said. "Now trying to fill Brian Urlacher's shoes is another story."

Tyrone Carter will fill in at strong safety for Pittsburgh, something he did previously in 2007, when Polamalu missed five games with a similar injury. It will be the 11th start of Carter's 10-year career.

"Any time he's ever stepped in, he's done as good a job or a better job," Polamalu said. "You couldn't imagine there would be any drop-off."

Carter won't bring Polamalu's freewheeling, blitzing style to the position, but he may need to stay home more often anyway given Cutler's strong arm and the deep speed of receiver Devin Hester.

The two hooked up for a 36-yard touchdown in Green Bay, but the rest of Cutler's much-anticipated debut didn't go well. Billed as the Bears' first franchise quarterback since Sid Luckman led the team to four NFL championships in the 1940s, Cutler threw a career-high four interceptions, including one on the first pass of a potential game-winning drive.

"Jay has to play better and he will play better," coach Lovie Smith said. "Some of the things he did in the game, we can't live with. His first preseason game he didn't play as well as he did his second preseason game. He'll get back off (to) a good start against the Steelers this week."

Ben Roethlisberger didn't get off to an impressive start in his first game since leading Pittsburgh on a game-winning drive at the end of Super Bowl 43. Roethlisberger took two sacks and threw a wobbly interception in the first quarter against Tennessee, but led a game-tying drive in the fourth before marching his team 63 yards in overtime for a game-winning field goal.

Roethlisberger threw for 363 yards -- his third-highest total ever and most in a Steelers win -- but Pittsburgh is concerned with a running game that forced its quarterback to throw the ball an unusually high 43 times.

The tandem of Willie Parker and Chicago-area native Rashard Mendenhall carried the ball 17 times for 25 yards, and the typically run-happy Steelers gained 36 yards as a team, their fewest in a win since 1982.

"I believe, particularly in September football, people make a commitment to stopping the run and it's easier to make the commitment when everybody feels good and you've got all the horses in the stable," said Tomlin, who lost twice to the Bears as the Vikings defensive coordinator in 2006. "... It's usually tough sledding early in the football season. That's been my experience."

Matt Forte averaged 2.2 yards on 25 carries in the Bears' opener.

Pittsburgh and Chicago last met in Week 14 of the 2005 season, a 21-9 Steelers home victory that was the first of eight straight wins on their way to winning Super Bowl 40.

The Steelers haven't visited Soldier Field since a 37-34 overtime victory in 1995, their lone win in 11 visits to Chicago.