JACKSONVILLE -- The New England Patriots made things interesting in the second half of their 31-20 loss to the Jacksonville Jaguars, but falling into an early hole highlighted the most disappointing part of the day: The defense didn’t build on its impressive season-opening effort.

The overall performance was subpar, and while there was a bit of a bounce-back in the second half, it sparks a question: As they prepare to visit the Detroit Lions -- a team led by their former defensive coordinator Matt Patricia -- exactly what are the Patriots on defense?

Are they the unit that swarmed in totaling 12 quarterback pressures and three sacks in a season-opening victory over the Houston Texans?

Or are they what they mostly showed against the Jaguars, when quarterback Blake Bortles carved them up?

“He did a number on us. We didn’t expect that,” said cornerback Eric Rowe, who relayed the unit expected more of a run-first approach from the Jaguars.

Credit is due to Bortles (29 of 45 for 377 yards, 4 touchdowns, 1 interception) and his pass-catchers. They were terrific, particularly in the first half.

At the same time, what had to frustrate coach Bill Belichick and the new leader of the defense -- linebackers coach Brian Flores -- was a series of mental mistakes specific to one of the key points of the game plan entering the game: Keeping Bortles in the pocket and not letting him beat them with his legs.

The Jaguars were 5 of 6 on third down in the first half, and one of those conversions on the opening drive came when veteran defensive end Adrian Clayborn rushed past him, opening up an easy rushing lane for Bortles to scramble 10 yards on third-and-7. Clayborn made a similar mistake in the second half, and then Bortles capped things off late in the fourth quarter with a 10-yard rush on third-and-8 (the Jaguars were 10 of 14 on third down in the game).

Meanwhile, Rowe's performance obviously wasn’t viewed favorably, because he was benched after two series in favor of veteran Jason McCourty. Rowe had been in coverage on Keelan Cole's 24-yard touchdown catch late in the first quarter. Earlier in the drive, Cole made a dazzling one-handed catch with Rowe in coverage.

“It hurts, but I wasn’t getting the job done,” Rowe said. “It’s hard to admit. It’s the NFL, there’s no time to sit and self-loathe, so I just have to go back to work at practice.”

Rowe didn’t take the field again until the second half, in a sub package, when the Patriots had to shuffle things around without safety Patrick Chung (concussion). Chung wasn’t the only starter to be knocked out, as defensive end Trey Flowers had sustained a concussion on the Jaguars’ opening drive.

Those were tough breaks, but nothing the Patriots haven’t been able to overcome in past years. Not on this day, however.

Rookie linebacker Ja'Whaun Bentley, who was one of the best players on defense in the opener, seemed to take a step back as he was exploited in the short passing game. Veteran linebacker Dont'a Hightower also looked a step slow. The pass rush, which was so potent in the opener, didn’t generate enough heat while the coverage from linebackers and the secondary was inconsistent.

“Obviously, any time you have a performance like this, it doesn’t leave a good taste in your mouth,” safety Duron Harmon said. “Obviously it’s the beginning of the season, but there’s no excuse for how we played. We have a long way to go and a lot of growth to continue to do -- and everyone is going to continue to try to get better.”

“It’s a little adversity you have to go through,” added cornerback Stephon Gilmore, who was one of the unit’s bright spots.

As Harmon and Gilmore said, given that it’s only the second week of the season, when no team in the NFL is a finished product, such struggles should be kept in their proper context.

Disappointing? For sure.

A cause for legitimate concern? Let’s give it more than two games before going there so decisively, but no doubt, it was what stood out most in the Patriots' loss.