As Bears’ defensive blueprint falters, can DC Sean Desai reinvent it against Steelers?

If the Bears had been forthcoming at the start of the season — and that’s not a strength of theirs, obviously — they would have said everything was riding on their pass rush.

General manager Ryan Pace and coach Matt Nagy knew they had made iffy moves in the secondary and hoped to negate those concerns with an overwhelming trio of outside linebackers Khalil Mack and Robert Quinn and defensive lineman Akiem Hicks up front. If opposing quarterbacks barely had time in the pocket, the Bears’ unproven cornerbacks wouldn’t need to hold their coverage long.

That plan worked for a while. But now it’s not.

The Bears didn’t have a sack or even a quarterback hit in the last two games, as the Buccaneers and 49ers combined to pile up 71 points. Tom Brady smacked them for a 109.8 passer rating, and Jimmy Garoppolo followed with a 100.6. Neither threw an interception.

In fact, the Bears have faced 107 consecutive passes without picking one off. And now they face the Steelers and 18-year veteran Ben Roethlisberger.

Roethlisberger is throwing the ball quicker than any quarterback in the NFL at an average of 2.37 seconds from snap to release, and the Steelers are tied for the 10th-fewest sacks allowed at 14 in 284 drop-backs. Roethlisberger has been pressured on only 20.3% of his drop-backs (fourth-best in the league) and thrown interceptions on 1.5% of his passes (seventh).

‘‘You don’t get to him,’’ defensive coordinator Sean Desai said. ‘‘People don’t get sacks in one second, right?

‘‘Sacks are a function of rush and coverage. You can’t have a breakdown in one and expect the other to be grea; that’s just not possible. We need to be tight [in coverage], and then when Ben gets to the second and third pump, we’ve got to get there. You better win on those chances [when he holds the ball for] three seconds.’’

The ground is crumbling beneath the Bears on both sides of that concept, though.

Mack was out last week because of a sprained foot and is very much in question for Monday after missing the first two practices this week.

And in the secondary, injuries and cost-cutting moves have forced the Bears to rely on the following:

• Cornerback Kindle Vildor, who is allowing a 147.4 passer rating in his first season as a starter.

• Cornerback Duke Shelley, who played sparingly on defense until this season.

• Safety DeAndre Houston-Carson, who has been predominantly a special-teams player in his six-year career.

• Safety Teez Tabor, who was on the practice squad a month ago.

• Safety Marqui Christian, who went five games without playing a snap on defense after a rough outing in the opener.

Again, the Bears could weather all of that reasonably well if their pass rush was as formidable as it was early in the season, when Mack and Quinn were both among the top 10 in sacks.

The two of them thriving simultaneously was a revelation for the Bears, who had no reliable threat to pair with Mack the last two seasons. Leonard Floyd didn’t contribute much in 2019, and Quinn was a dud last season after signing a five-year, $70 million contract.

Their underperformance left Mack consistently facing double- and triple-teams, and he dropped to single-digit sack totals for the first time since his rookie season. With the effect of Mack mitigated, the Bears were 22nd in sacks, 25th in takeaways and 11th in opponent passer rating over 2019 and ’20.

If Mack remains out or limited, Quinn will be the Steelers’ priority. He got a taste of that in his 52 snaps against the 49ers.

‘‘I don’t want to say ‘rough’; it was just football,’’ said Quinn, who has 5½ sacks. ‘‘Khalil is great — I would say probably a Hall of Famer — but you can’t put all of your money on him. We’ve got 10 other guys out there who get paid to make plays, too, so everyone has to step up.

‘‘You’ve just got to do a little bit more, strain a little bit harder. They’re not going to allow you to have a great day easily. . . . Taking on two, three every play is going to be . . . not impossible, but it’s going to be tough.’’

It’s going to be tough to overcome all that’s working against the Bears, too. Between personnel attrition and the Steelers’ quick-pass offense, they probably will need a different formula defensively.

That’s Desai’s job. It requires constant reconfiguring throughout the season, and this won’t be the last time the Bears need him to innovate.