Patrick Peterson admitted Arizona's defense had its guard down in Sunday's loss. Ross D. Franklin AP Photo

Watching the Pittsburgh Steelers send out third-string quarterback Landry Jones midway through the third quarter, the Arizona Cardinals' defense admitted a bit of complacency set it.

"I thought when a third-string quarterback comes in, they were going to run the ball," Cardinals defensive end Calais Campbell said. "It caught us off guard a bit."

More from FoxSports

Indeed it did. Jones replaced an injured Michael Vick and threw an eight-yard scoring pass to Martavius Bryant on his second pass attempt to put his team ahead to stay in an eventual 25-13 victory for the Steelers.

"A lot of times you get comfortable, you may get lackadaisical, you may not get a call that you want -- it all kind of affects the way you perform going forward," Arizona safety Tyrann Mathieu said.

Vick was 3-of-8 for only six yards when he went to the sideline in a game the Cardinals were dominating - yardage-wise - by a wide margin. Jones changed the tenor of the contest and finished 8-of-12 for 168 yards and two TDs, including a late 88-yard strike to Bryant that provided the dagger.

"He's an NFL quarterback for a reason," Cardinals cornerback Patrick Peterson said. "We just let our guard down just a little bit. If you want to be a great defense, we can't do that. We have to make sure we keep our foot on the pedal at all times, no matter who is at quarterback. We have to make sure we stay focused for all 60 minutes and we didn't do that."

MORE NEWS: Want stories delivered to you? Sign up for our NFL newsletters.