The Chicago Bears' running back needs surgery after injuring his left ankle Sunday — another setback for the team's first-round draft choice in 2005.

Benson, who took over this season as the Bears' starter after the trade of Thomas Jones to the Jets, broke free for a 21-yard run in Sunday's game against the Denver Broncos.

But he was hurt as he landed while being tackled by Denver safety Hamza Abdullah and later had to be carted off the field following the second-quarter play.

"It's tough when you lose your starting tailback. Cedric went down with a season-ending injury, which is a tough break," Bears coach Lovie Smith said today, the day after the Bears beat the Broncos 37-34 in overtime.

"He went out on a good run. He had put together two good weeks. ... We'll miss him."

Veteran Adrian Peterson will now move up to the starter's role with rookie Garrett Wolfe the backup. Peterson had 45 yards on 17 carries Sunday, including a 4-yard TD run during the Bears' fourth-quarter comeback from a two-touchdown deficit. He also caught five passes.

"You could say he's a guy who deserves the opportunity to get more playing time," Smith said of Peterson. "He's done everything we've always asked him to do."

Benson gained 47 yards on eight carries before he was hurt Sunday. He'd rushed for 674 yards this season on 196 carries, an average of 3.4 yards per carry and had four touchdowns.

Benson had taken his share of criticism for the lackluster performance of Chicago's running game, one that is averaging only 3.3 per carry. But a week earlier against Seattle, he showed the form that made him a star at Texas when he broke off a 43-yard TD run. It was the longest run in a career that has been slowed by injuries.

"He had a good game against Seattle last week and the run he went out with was a good run," Smith said. "We rushed over 100 yards yesterday and with him you never know what we would have been able to do.

"If you look at his play there was definitely improvement that he's made so that's the light coming on, I guess you would say that. I just know that he had made improvement and he was feeling more comfortable in his role by the production he was having."

Asked if the Bears regretted trading Jones — who had more than 1,000 yards in each of the previous two seasons in Chicago — Smith said: "We don't have Thomas Jones here. This is the group we have and we feel comfortable with it."

A lengthy contract negotiation caused Benson to miss his first training camp two years ago, and a knee injury knocked him out of six games that season.

In 2006, Benson sprained his shoulder during training camp. He went on to become a strong backup to Jones, gaining 647 yards and averaging 4.1 yards per carry. In the Super Bowl, however, he was knocked out of the game in the first quarter after hurting his knee.

Now the Bears will turn to Peterson, who has 189 yards on 52 carries. He also had 33 receptions, tied for second most on the team.

The Bears' victory Sunday kept their slim wild card chances alive in the wide open NFC, even at 5-6. They face the Giants this week at Soldier Field, looking for their first two-game winning streak.

Devin Hester had a 75-yard punt return and an 88-yard kickoff return, both in the third quarter against the Broncos.

"Seems like every time we need a boost, he's the guy that steps up to the plate," Smith said.