PITTSBURGH -- It's easy to cite the Pittsburgh Steelers' franchise-record 56 sacks and a top-five scoring defense for much of the year as positive steps in a defensive rebuild. But while the defense produced enough to help win 13 games, the failure to translate those improvements to the postseason leaves lingering questions for a group stocked with former first-round picks.

Never was that more evident than when the Steelers bit miserably on a play-action, leaving fullback Tommy Bohanon wide open in the end zone for a 14-yard score with 4 minutes, 19 seconds left in Sunday's AFC divisional-round defeat to the Jacksonville Jaguars. This was a theme all day -- running backs and tight ends and fullbacks getting free in space thanks to what looked like blown coverage or an over-commitment to the run.

That shouldn't happen against top-five passing offenses, let alone Jacksonville's 17th-ranked attack. Blake Bortles outplayed his game-manager role Sunday in part because the Steelers encouraged that.

Words from the locker room painted a picture of poor discipline and confusion. Defensive end Cam Heyward noted that the Steelers' identity all season was one of players staying in their gaps and rallying to the ball. They did neither well on the biggest stage.

"Rust didn't play a part," Heyward said. "Execution played a part, not trusting that everybody is going to be in their gaps."

Added linebacker Bud Dupree: "We have Ben Roethlisberger at quarterback. We’re supposed to make a stop, give them a chance. We didn’t."

The most jarring quote came from Mike Tomlin on why he tried an onside kick with just over two minutes left and down seven: "We hadn’t stopped them convincingly enough to take any other approach in my opinion, and it was my decision."

That's one harsh reality.

Fifteen different Steelers recorded a sack in the regular season. None of those players got one Sunday, when Pittsburgh allowed three first-half rushing touchdowns in a playoff game for the first time in franchise history.

The Steelers knew the run was coming and yet still allowed 164 yards while forgetting to cover the underneath routes that became chunk yardage for Jacksonville. T.J. Yeldon's 40-yard streak down the sideline in the fourth quarter for one of Jacksonville's eight third-down conversions was especially egregious.

Several Steelers players say they weren't looking ahead to New England. Even if that's true, they clearly fueled Jacksonville's play with the perception that they were planning for next weekend's AFC title game.

Perhaps something else was at play -- a defense running out of gas, forcing the Steelers to answer tough offseason questions about how good they really are.

Heyward, Stephon Tuitt and T.J. Watt are building blocks. Vince Williams grew into a key starter at inside linebacker, but the team's depth was shot once Ryan Shazier went out. Dupree, who played hurt for most of the year, didn't have the big season he wanted. Artie Burns had two pass deflections earlier in the game but was emotional in the locker room after giving up a 45-yard pass play to Keelan Cole in the fourth quarter. That encapsulated his up-and-down year.

The Steelers must determine how all these pieces should work to improve a defense that has been at its worst in Pittsburgh's past two playoff games.