By Dan Durkin-

(CBS) When the Bears’ 2013 season ended on a frigid night last December, the focus quickly shifted to curing the team’s ills, which were painfully obvious — resurrect the league’s worst run defense and pass rush. With problems so acute, it was nearly impossible to go wrong, as help was needed at every level of the defense.

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The Bears acted accordingly, spending $35 million guaranteed on three defensive ends, dedicating their first three draft picks to defensive players and bringing in two new defensive assistants with more than a decade of NFL coaching experience.

Yet, when they kicked off the season Sunday against the Buffalo Bills — a team that has one winning season over its past 14 — the same issues remained. The Bills had their way with the Bears’ run defense, racking up 193 total yards at a clip of 5.8 yards per carry. Quarterback EJ Manuel was sacked only once as the Bears dropped their season opener 23-20 in overtime.

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Despite it being a passing league, the blueprint to beat the Bears is run the ball. Over their past 11 games, the Bears are 4-7 and their opponents have run the ball more than they’ve passed it in seven of those games, averaging 190 rushing yards per contest.

In football, you earn the right to rush the passer by stopping the run, which is something the Bears simply haven’t figured out how to do.

It wasn’t a secret that the Bills liked to run the ball. In 2013, they led the league with 546 rushing attempts. On Sunday, they exploited the Bears with zone read and split zone plays.

In their third preseason game against the Seahawks, the Bears’ overall lack of speed on defense raised concerns about the age of the group finally catching up with them. On Sunday, the Bears were unable to recover from misreads and were beat to the perimeter, which led to extra yardage.

Bears linebackers frequently missed their fills on zone read plays and jumped out of the hole, leaving gaps unmanned at the line of scrimmage. Eye discipline is such a critical component of playing linebacker in the NFL, and both Jon Bostic and veteran Lance Briggs were guilty of guessing wrong and overreacting on initial play fakes.

Not only were the Bears beaten schematically on gash plays, they were also physically beaten in the trenches. The Bears’ defensive line didn’t anchor and hold the point of attack, which allowed Bills running backs to get through the first two levels of the Bears’ defense unscathed.

The safety position remains unsettled as the Bears used a rotation. In both free agency and the draft, they were presented opportunities to raise the talent level at the safety position and twice they prioritized other positions.

Free safety Chris Conte baited Manuel into throwing an interception, which the Bears converted into a touchdown. But he also had a few missed tackles and seemed to be indecisive at times about playing the ball or the man.

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Looking ahead, the Bears’ next four opponents all finished in the top 11 in rushing offense. So, until they prove they can stop the run, teams will continue to pound away at their front and if they’re successful, they’ll keep the Bears offense on the sidelines.

Speaking of the Bears offense, they did the defense no favors on Sunday. They moved the ball, but costly turnovers (one fumble, two interceptions) led to 10 points for the Bills.

Quarterback Jay Cutler signed a lucrative contract extension in January. The guaranteed money he’s owed in 2014 — $18. 5 million — is the third-highest figure in the league. putting him ahead of six of the last eight Super Bowl-winning quarterbacks. Cutler’s first interception appeared to be a miscue between he and tight end Martellus Bennett, which can be cleaned up. However, plays like Cutler’s second interception simply don’t match his pay grade.

With eight minutes remaining in the game and the score tied 17-17, the Bears faced a third-and-1 at the Bills’ 34-yard line. Trestman dialed up a quarterback bootleg, giving Cutler a run-pass option. The play fake got the Bills’ front to move, but the coverage stayed with the Bears receivers. Cutler rolled to his right and instead of living to play another down, he forced the ball across his body to the middle of the field into the waiting arms of Bills defensive tackle Kyle Williams. Nine years into his career, this is simply an unacceptable decision by Cutler.

It’s fair to question whether any sort of coaching will be able to break Cutler of these habits, which have defined his career.

In 2013, the Bears enjoyed fortunate health on the offensive line. They were one of three teams to have the same five starters for all 16 games, but they weren’t as fortunate Sunday. Both left guard Matt Slauson and center Roberto Garza were lost with ankle injuries, forcing reserves Michael Ola and Brian de la Puente into action. To their credit, Ola and de la Puente filled in admirably.

The injury bug wasn’t limited to the offensive line. Wide receiver Brandon Marshall twisted his right ankle, and Alshon Jeffery tweaked his right hamstring. Marshall tried to tough it out for the remainder of the game, but it was clear he was hampered by the injury.

The Bears heavily use three-wide receiver personnel groupings and were forced to play long stretches of the game with the likes of Santonio Holmes, Micheal Spurlock and Josh Morgan.

The rash of injuries tested the Bears’ depth and impacted coach Marc Trestman’s play-calling and formations. The severity of all the injuries suffered Sunday will be closely monitored, as they could easily derail the early portion of the season, during which the offense must carry the team as the defense — hopefully — takes shape.

This was a winnable game the Bears let slip away. They had mental errors, penalties that wiped out first downs and lost the turnover battle. The positive is there’s 15 games left in the season, but the way this game was lost was very reminiscent of last season.

With three of their next four games against 2013 NFC playoff teams and six of their next eight games on the road, you’ll quickly know what this team is made of.

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.