ARLINGTON, Texas -- Tony Romo never took off his baseball cap. Miles Austin, Dez Bryant and Jason Witten didn’t set foot on the field.

And still, the floundering Dolphins secondary managed to struggle in Wednesday night’s 30-13 loss to Dallas.

The Cowboys’ big guns remained in the holster for the preseason finale. Starting quarterback Romo was held out in preparation for Dallas’ season opener next Wednesday at the New York Giants, while top receivers Austin, Bryant and Witten were in street clothes recuperating from injuries.

Meanwhile, against the likes of third-team quarterback Stephen McGee and receivers Dwayne Harris, Andre Holmes and Danny Coale, the Dolphins’ defensive backs allowed two pass plays of more than 30 yards in the first half — one of which set up a touchdown — and were hit with three of the team’s five first-half penalties for a total of 72 yards.

For a team that entered the night allowing opposing passers to post a 99.9 rating in three preseason games, the NFL’s fourth-worst mark, Wednesday’s performance wasn’t exactly a confidence-builder, especially in the wake of this week’s trade that sent cornerback Vontae Davis to Indianapolis for two draft choices.

Indeed, the man who made Davis expendable, veteran cornerback Richard Marshall, made his share of missteps in his two series on the field. When Dallas running back Phillip Tanner got the corner on a stretch play to the left, Marshall stopped him by the back of his shoulder pads, drawing a 15-yard penalty for a horse-collar tackle. On the next snap, Kevin Ogletree muscled past Marshall for position on an out route, though the catch was negated by a holding penalty in the backfield.

Marshall mercifully spent the rest of the evening on the bench. The man who replaced him at left cornerback, Nolan Carroll, wasn’t so fortunate. Carroll actually had his moments, finishing the game with four tackles and two pass breakups, but he and young hopeful Quinton Lawrence staggered through a second quarter in which the Cowboys scored 20 points and the Dolphins helped make McGee, who is likely to be released before the season begins, look like an actual NFL quarterback.

“Yeah, he is playing hard, but as a team we are getting outplayed,” Dolphins coach Joe Philbin said of Carroll. “It was a poor second quarter, all the way around, in all phases of the game. We gave them seven points and penalties and sloppy performances in the second quarter.”

The problems actually began in the final minute of the first quarter, when Lawrence broke up a deep pass for Ogletree but was flagged for a 43-yard pass interference call. That led to Dallas’ first score, a 25-yard field goal.

On the Cowboys’ next possession, Carroll was beaten for a 32-yard completion from McGee to Holmes on a deep sideline route on third down, and was outfought for the ball by Benford on a short pass.

Lawrence’s troubles continued into the second half -- he was hit with his second interference penalty of the night early in the fourth quarter.