Late in the first half Sunday at San Francisco, defensive tackle Darnell Dockett, needing a breather, signaled for a replacement.

Onto the field raced Calais Campbell, the Cardinals’ 22-year-old rookie, for his first NFL play.

He managed to line up just before the snap.

The 49ers gave the ball to running back DeShaun Foster. Campbell fended off a blocker and managed to make the tackle; in fact, Foster barely made it back to the line of scrimmage.

This is the sort of depth the Cardinals boast these days on defense thanks to some key offseason additions.

Consider that at the key pass rushing spot — a combination of right defensive end/linebacker — new Cardinal Travis LaBoy had two sacks, a forced fumble and a fumble recovery.

His backup, holdover Bertrand Berry, had a sack and forced a fumble.

The Cardinals ended up with five turnovers (their offense had none), the sort of performance that nearly guarantees a win. And they did, 23-13.

“Me and Bert are the same player,” LaBoy joked. “We can’t be on the field at the same time.

“There’s no first or second string.”

LaBoy was a sort of under-the-radar player at Tennessee, sharing time with Pro Bowler Kyle Vanden Bosch, as the Titans had a dominant defense.

In Arizona, the Cardinals “match up just as well as in Tennessee” in terms of defensive talent, LaBoy said.

“The depth has made a difference,” said defensive coordinator Clancy Pendergast. That, “And we’re together for another year.”

Berry, pointing to the team’s linebacker group, said, “It’s exciting to think we have eight guys who can come in at any given time, get after the quarterback and not have anybody spent in the fourth quarter.”

Defenses will line for up to 70 plays, Berry pointed out.

“That’s too much to ask … be relentless for 70 plays. You have to get a break.”

With the Cardinals’ defense, “You know the guy behind you will do the same thing,” Berry said. “It’s a good situation to be in.”

In practical terms, the depth could mean the sad, old days of getting blown out are over, that the Cardinals will have a shot to win just about every game they play.

“It’s just one game,” cautioned safety Adrian Wilson.

At the same time, he acknowledged, “We have a lot more pieces. We have guys who can do a lot of things well.”

From now on, “It’s about staying healthy through the season, being able to roll guys out to keep us fresh.”

At the moment, the Cardinals are just about at full strength.

Said Berry, “It makes for an explosive defense and a consistent defense.”

Defensive end Antonio Smith, who started to blossom last year, credits the team’s increased experience with the modified 3-4 defense.

“Last year, was our first time running it. This year, we’re honing it. ... It’s like coming home. We know what is expected. We know the holes and weaknesses in it.”

The result seems to be the Cards’ defenders are playing faster, without having to think as much.

“We want to establish that we’re going to be relentless,” Smith said. “We’re going to play physical.”

Linebacker Karlos Dansby, who developed into a star-caliber player last year, believes the team grew up last year in a series of close losses.

“Now we’re going to come out on top. … We can really play the game on this side of the ball.”