Ahmad Brooks and the 49ers D has been a shell of their former self this season. (USATSI)

They were once feared on third down.

 

Their suffocating run defense put quarterbacks in unfavorable third-down situations, which turned into advantageous ones for the San Francisco 49ers defense.

 

They got after the passer.

 

They aren't anymore.

 

If you want to pinpoint why the 49ers are 1-2 heading into this week's game with the Philadelphia Eagles, the thing that stands out the most is a lack of a pass rush.

 

It used to be magical, but the magic is reversed now: They actually turned Drew Stanton into Drew Brees last week.

 

Stanton, the Arizona Cardinals backup quarterback, torched the San Francisco defense, throwing two touchdown passes and completing pass after pass deep down the field.

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That takes time.

 

He had so much time on some plays he could have taken out a lawn chair, put on some lotion and soaked in the Arizona sun -- if the roof were open, that is.

 

Here's how bad it is for the once feared 49ers defense: They are last in the NFL in third-down defense. Last. Teams have converted 51.6-percent of their third downs against the 49ers, including several because of penalty. By comparison, the 49ers were sixth in third-down defense last season, holding teams to a 34.1-percent conversion rate.

 

After holding Arizona to 2-for-6 on third down in the fist half last week, the Cardinals were 6-for-7 in the second half. Included in that total were two conversions by penalty, a 21-yard touchdown pass, a 45-yard completion and a 20-yard run to ice the game.

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In their last two games, San Francisco has given up 38 points in the second half, including five passing touchdowns. The 49ers are 17th in scoring defense, 22nd in sacks with just four.

 

Who are these guys?

 

I know they are missing pass rusher Aldon Smith and inside linebacker NaVorro Bowman, two of the best at their positions in the league. But all we heard the past few years was how the 49ers were built to handle personnel losses. They had depth. They had young players ready to take over.

 

So far, it isn't working. Smith's absence really shows up. He is suspended for nine games for violating the league's personal-conduct policy, but the 49ers thought Ahmad Brooks would help fill the role as their top pass rusher. They also had hopes that Corey Lemonier, a second-year player from Auburn, would step in and provide the speed off the edge.

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In three games, those two have combined for one sack. Brooks, who has been considered underrated with Smith on the other side, is finding the going tougher when he's in the lead role. With no elite pass rusher on the other side, he is getting more attention -- and he isn't winning as much.

 

Lemonier has the look of a one-trick pony: Straight up the field. Even when the 49ers use their patented tackle-end stunt, with Justin Smith doing his usual grab-and-hold on the guard to allow the end to loop inside, it isn't working.

 

The 49ers are not a blitz team, but they blitzed 13 times last week. That didn't get home either.

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They clearly miss Bowman's speed in coverage and in the run game. He is arguably the best inside linebacker in the league. They also are without nose tackle Glenn Dorsey, who is out with an injury, but Ian Williams actually did a nice job on the nose last week.

 

The secondary, without the pass rush, is struggling. Safety Eric Reid, who impressed as a rookie last season, has really struggled. He doesn't look like the same player. With starting corner Tramaine Brock out the past two games and playing only 11 snaps in the first game, the corners haven't been as good as in the past.

 

Here's a look at a touchdown pass Stanton threw to rookie John Brown. The play shows a lot of the problems for the 49ers.

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Play: Arizona first-and-10 at San Francisco 24 with 9:25 left in the third quarter.
Offense:  Posse (Three WR, 1 TE, 1 RB) -- bunch to the left.
Defense: Nickel,  (three-deep, four-under zone, four-man rush).

   
(NFL Rewind)

Before the snap, the Cardinals motioned Brown (circle) from the outside to inside of  receivers Michael Floyd and Larry Fitzgerald. At the snap, both Fitzgerald and Floyd threatened deep, which froze Reid in the deep middle. Brown, with a free release, was able to run past the linebackers for an easy pitch-and-catch with Stanton.

(NFL Rewind)

As you can see from the end-zone shot and the GIF, Stanton had a clear throwing lane and good vision to hit Brown behind the linebackers, who both seemed way too occupied with tight end John Carlson.  But look at that protection. Nobody is even threatening to dump Stanton.

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Here's a look at another third-down conversion, this time in the run game. It came with Arizona trying to bleed the clock to ice the game and San Francisco needing a stop to get the ball back.

Play: Arizona with a third-and-6 from the Arizona 31 with 2:19 left in the game.
Offense: ACE  (2 TE, 1RB, 2 WR)
Defense: Base (3-4 front, single safety, eight-man box).

   
 (NFL Rewind)

This is a play that shows how much they miss Bowman. In an obvious run situation, the Cardinals get good blocks on Williams and Justin Smith, but that should have freed up the linebackers to make the play.

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 (NFL Rewind)

 The problem was Willis guessed wrong and attacked the "B" gap and got caught up in the wash of the Smith block. He could not get back to make the play. Michael Wilhoite, who is filling in for Bowman, couldn't get off a block by center Lyle Sendlein.

 

Fitzgerald came down and got a piece of safety Antoine Bethea, and Ellington scooted through for a 20-yard run.

 

As the 49ers move forward, starting with a tough challenge this week against the high-flying Eagles' offense, it will be interesting to see what changes are made. Do they blitz more, even if that isn't their character?

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The Eagles are banged-up on the offensive line, so that could help amp up the pass rush this week and might not force the 49ers to blitz. If the 49ers don't get any pressure on Nick Foles, though, those third-down numbers will again be bloated and they could be staring 1-3 in the face.

 

Who is this defense? It certainly doesn't look like anything we've come to expect from the 49ers. Without Bowman and Smith, it's just not as scary.

 

The scheme is the same, but their current plight reminds us of that old football adage. It usually goes like this: It's not the Xs and Os, but it's the Jimmy and Joes. For the 49ers, it's more like it's not the X and O, but Aldon and NaVorro.

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More Stuff I saw on tape

 

J.J. Watt Play of the Week: Every week in this space we feature a play from Houston defensive end J.J. Watt. He is the game's best defender -- no doubt -- but he's been blocked some this season in one-on-one situations as well. The Texans are 31st in the league in yards per rush allowed, but it takes more than just Watt. The Giants used an unbalanced line last week to help run right at Watt on one series. Normal right tackle Justin Pugh flopped over to the left side outside of left tackle William Beatty. And they ran it that way with success. On back-to-back plays, Pugh, a second-year tackle, did a nice job on Watt in the run game to spring Rashad Jennings. But then Watt got even. He beat Beatty with a quick move to drop Jennings for a 6-yard loss. You can contain him for a while, but he always seems to come up with a big play. Here's a look at his play on Jennings.

   

Tyron Smith is proving he's worth the price: The Cowboys gave left tackle Tyron Smith a huge contract in the offseason. He showed why against St. Louis Rams defensive end Robert Quinn last week. He dominated Quinn all day long. Whether in the run game or the pass game, Smith got the best of Quinn, a player I consider the best outside pass rusher in the league. Smith played strong and with great technique in handling Quinn's speed. On several pass plays, he just rode Quinn around the corner and took him past quarterback Austin Davis. He threw him down on one pass rush when Quinn tried to get inside of him. In the run game, Smith pushed Quinn around. He opened up some big lanes with a strong base and good power to move Quinn out of the hole.

At 23, Smith might be on his way to being considered the best left tackle in the game. As for Quinn, I still can't believe he is without a sack. He's a player I expected to get close to 20 again after getting 19 in 2013. There was, though, one play that stood out from Quinn's game last week. He was unblocked on a run designed to go inside of him. He charged up the field, and DeMarco Murray ran inside of him as Quinn scrambled to get back to make the tackle. He got a hand on him, but missed. Quinn than continued to run up the field after Murray and was able to get in front of him and tackle him after a 20-yard gain. Unreal. But for the most part, Smith was a big winner in this battle of young stars.

 

Bengals OL is the real deal: Why are the Cincinnati Bengals 3-0? Yes, the defense has played really good football. And Andy Dalton isn't turning it over. But a real secret to the success is the play of the offensive line. They haven't allowed a sack, and they are good in the run game. Rookie center Russell Bodine had his best game last week against the Titans. On successive goal-line plays, one a sneak by Dalton, he put Titans nose tackle Sammie Lee Hill on his back. Yes, on his back.

With Bodine improving in the middle and tackles Andre Smith and Andrew Whitworth off to good starts, the Bengals have one of the better lines in the league right now. Whitworth never seems to get the due he deserves as one of the best left tackles, bit Smith's improvement over the years is impressive. He's come a long way from the chubby kid everybody laughed about at his pro day at Alabama. It will be interesting to see this group in a week when they play the Patriots. One more thing: They played without guard Kevin Zeitler last week, and he was off to an impressive start.

 

Weddle's play continues to impress: Seattle's Earl Thomas is considered the best safety in the game. But I will say this: San Diego's Eric Weddle isn't far behind. I have been a big proponent of Weddle's play, even when he sometimes gets overlooked. Weddle is off to a great start this season, playing better than any safety in the league. Weddle was all over the field last week against the Bills. Weddle can drop down as an eighth man in the box and despite being a former college corner, and he's physical enough to make plays. He also has good range, better than most safeties, in the passing game.

On the Bills' second series last week, Weddle lined up deep as a Cover-2 safety. But before the snap, he dropped down and loaded the box on the right side of the defense. The Bills tried to run C.J. Spiller inside, away from Weddle, but the safety came down and dropped him for a 1-yard loss with a great play off the edge. Later in the fourth quarter, the Bills tried a screen to the explosive Spiller. Weddle had the force on the play, and was blocked. But he stayed with the play and when Spiller tried to cut to the outside, Weddle was able to chase him down. It was a 25-yard gain, but if Weddle doesn't get off the block to get back into the play it might have been a touchdown. Later in the quarter, he blew up Marquise Goodwin on a crossing route. The throw was behind Goodwin, and Weddle lit him up for an incomplete pass. Weddle is smart. He is tough. He is a good tackler and he can run and play coverage. It's time he gets the due he deserves.