ARLINGTON, Texas — The Saints waited all day for Sunday night.

Maybe they waited a bit too long.

For more than a half, the high-powered New Orleans offense disappeared Sunday night at AT&T Stadium. The Saints failed to score in the first half and went to the locker room trailing 24-0, marking only the third time they’ve been shut out since Sean Payton became head coach in 2006.

Curiously, the last first-half shutout came in 2011, the year New Orleans set a record for most yards gained in a season. On Oct. 30 of that year, the Saints trailed 17-0 in a game they eventually lost, 31-21, at St. Louis.

An early hole

For the first time this season, the Saints allowed their opponent to score on its opening possession. Dallas took the opening kickoff and blasted 80 yards for a touchdown, taking 12 plays and 7:10 off the clock before Terrance Williams scored on a 6-yard pass from Tony Romo.

The last time a New Orleans opponent scored on its first possession was the last game of last season, when Tampa Bay scored on a flea-flicker pass from Mike Glennon to Tiquan Underwood.

The Cowboys’ touchdown was just the beginning of a horrendous first half for the Saints’ defense, which allowed Dallas quarterback Tony Romo to complete his first nine passes for 86 yards and a touchdown and gave up 87 yards rushing to DeMarco Murray.

Romo finished the half 17-for-22 for 202 yards with two TDs and a 135.0 rating as the Cowboys piled up 290 yards of offense, the most allowed in the first half by the Saints this season and just short of their 2013 season average for a full game — 305.7 yards per game.

Armstead out

The Saints’ offensive line took a blow — literally — in the first quarter, when left tackle Terron Armstead was hit in the head on a first-quarter running play and wobbled off the field.

The 6-5, 304-pound tackle, a third-round draft choice last season from Arkansas-Pine Bluff was taken to the locker room, where it was determined he had a concussion and would not return. He was replaced in the lineup by Bryce Harris.

Trouble with Terrance

While Dez Bryant is by far the Cowboys’ biggest receiving threat, the Saints actually managed to keep him quiet. Through three quarters, Bryant managed a mere two catches for 26 yards even though Dallas threw several deep balls in his direction — cornerback Keenan Lewis broke up one and had tight coverage on two others.

Williams, on the other hand, was a problem all night. The second-year wideout from Baylor led the Cowboys through three quarters with six receptions for 77 yards and two scores, beating Corey Walker on a slant in the end zone in the first quarter and outfighting Brian Dixon for the ball.

Goodwin back

The good news up front was the return of center Jonathan Goodwin, who suffered a high left ankle sprain in last week’s victory over Minnesota.

The 13-year veteran missed the entire week of practice but was back in his usual spot as the starter Sunday night.

Lagniappe

Ron Leary, a product of Baton Rouge’s Southern Lab High School, started at left guard for the Cowboys. It was the lineman’s 19th consecutive start for Dallas.