The effectiveness of a defense can be judged in many ways. The Patriots like to look at the bottom line. They consider points allowed as the truest measure.

In that regard, their defense has often been referred to as “bend, but don’t break.” Opponents often haven’t had too much trouble moving the ball, but the Patriots tend to make stops before too much damage is inflicted.

Ultimately, this puts stress on the unit in the red zone, but more importantly, Bill Belichick’s defense lives and dies by what happens on third down. Can they get off the field? Can they give the ball back to Tom Brady and the offense without surrendering points?

They were 21st in third-down defense last season, allowing 82 conversions on 208 attempts (39.4 percent). Not awful, but it’s nothing to brag about. The Super Bowl, on the other hand, was a complete disaster. The Eagles were 10 of 16 (63 percent) on third down and 2 for 2 on fourth down.

So even though the Patriots wound up fifth in the league in points allowed – just 18.5 per game – the fact that they couldn’t consistently make stops came back to bite them. Third down was where the Super Bowl was lost.

“That’s always going to be our focus,” said safety Devin McCourty. “Our goal is to not allow points, but it all trickles down. Third down is always an emphasis. You win and lose games on third down.”

Linebacker Kyle Van Noy said last week the Patriots defense was going to “show up” a lot of people and quietly surprise the critics. They won’t be able to surprise anybody, if they can’t get off the field on third down.

Nick Foles and the Eagles certainly found the recipe to pick apart the unit. Runs, screens, play-action passes, deep balls, trick plays. Whatever was called worked.

Blake Bortles, of all quarterbacks, nearly beat the Patriots in the AFC championship game. The Jacksonville signal-caller converted 6 of 15 of his third-down attempts, and it took a brilliant diving pass breakup by Stephon Gilmore on a fourth down to end a last-ditch Jaguars threat.

“We need to get better at everything, but obviously, third down is a big part of the defense,” said Gilmore. “If you don’t get off on third down, you’re not going to be good on defense. We really focus on a lot of stuff. We’re just taking it one day at a time, and trying to get better.”

Belichick addressed third down with the defense during training camp practices last week. There were situations that were worked on and stressed.

Said safety Duron Harmon: “We know we have to improve on it to be the team we want to be.”

Being better on third down actually starts on first down. The Patriots can’t give up long gains and set up easy conversions. Six of the Eagles’ conversions only needed four yards or fewer.

The addition of tackle Danny Shelton was about winning the trench wars, stopping the run on those early downs and setting up more favorable third-down situations.

“You can’t have a good third down until you have a good first down,” said Gilmore. “You have to take it one play at a time. Focus on what down it is. Try to make plays and get off the field.”

Added McCourty: “If you’re team lives on third-and-1 or third-and-2, it’s not going to be a great year for you on third down.”

Cornerback Eric Rowe hopes the defense tighten up before the red zone. Last season, the Patriots struggled with coverage breakdowns and miscommunications, leading to big plays.

“It’s a mindset,” said Rowe. “We need to start fast, get them in second-and-10, third-and-long. It’s really just playing better on the early downs and starting faster. We just didn’t get it done last year.”

Bend-but-don’t-break defenses have won for the Patriots in the past. Having Brady does that. He can cure a lot of ills.

But as everyone witnessed last year, even an MVP performance by the quarterback doesn’t always bail out the defense.

Right out of the gate Thursday night in the preseason opener, the defensive regulars didn’t show much against Washington. It’s hard to make any snap judgments in a preseason game, but it’s still worth noting the defense still has plenty of work to do.

Belichick and de facto defensive coordinator Brian Flores had many of their top front-seven players – Dont’a Hightower, Deatrich Wise, Malcom Brown, Shelton, Adrian Clayborn – still taking snaps in the second quarter. Washington had no problem moving the ball, with 201 yards passing between Colt McCoy and Kevin Hogan, plus 60 yards rushing before the half.

And, right on cue, one of the pivotal plays was a third-down completion, a 25-yard scoring pass on third-and-11 from McCoy to running back Byron Marshall, who beat Van Noy coming out of the backfield.

“We want to be better, we want to be a great defense,” said Gilmore. “Whatever way it takes to win, that’s what we want to do in the end. Third down, first down, red zone, we have to do whatever it takes to win.”