After winning five straight "must-win" games, the Dallas Cowboys (8-6) laid an egg in the first game they didn't have to win. The Cowboys were thoroughly dominated on the road, 23-0, by an Indianapolis Colts (8-6) team that needed a win to stay alive in the AFC wild-card race.

The Cowboys' offense didn't have trouble moving the ball at times against the Colts, but penalties and overall ineptitude in the red zone cost the team valuable scoring opportunities, especially in the first half. The Cowboys were limited by injuries to their interior offensive line, as Zack Martin missed the game and Xavier Su'a-Filo exited in the first half because of an eye injury, but poor execution was the real reason for Dallas' offensive struggles.

The Dallas defense had one of its worst showings of the season, as Andrew Luck matriculated the offense down the field through the air while Marlon Mack punished the Cowboys' front seven on the ground. The Cowboys' front seven really struggled, failing to apply much pressure to Luck or beat blocks in the run game. Because Indianapolis was effective running the ball on early downs, it was able to take advantage of its favorable third-down situations, going 8 for 11 on Sunday.

The Cowboys once again struggled with penalties as they were called for nine flags that resulted in 74 yards, making it the second straight week they had at least nine penalties.

Making matters worse, the Cowboys failed to clinch the NFC East on account of Washington's 16-13 win over Jacksonville. With that in mind, let's take a look at a few things gleaned from Dallas' loss:

Colts dared Cowboys to run -- and it worked

Throughout the entire season, teams have loaded up the box to stop Ezekiel Elliott and the Cowboys' running game, content to allow Dak Prescott to try to beat them through the air.

The Colts decided to flip that game plan on its head, playing with two deep safeties and light boxes against the Cowboys' offense. The Colts were fine with the Cowboys churning yards on the ground as long as they made life as difficult as possible for the Cowboys wide receivers. With injuries up front putting an artificial ceiling on Dallas' rushing attack, the Colts were wise to sell out to stop the pass. The only times Indianapolis really sold out to stop the run were in short-yardage situations, and that was all that was really necessary, as Dallas' passing attack struggled throughout the game.

For the first time all season, a defense made stopping Prescott (and maybe more importantly, Amari Cooper) its No. 1 priority -- not Elliott -- and it worked to perfection.

The Cowboys were able to put together multiple drives of 10-plus yards on the back of Elliott and a short passing game to the tight ends, but the offense, as it has all season, sputtered once it crossed the 50-yard line, wasting multiple scoring opportunities with penalties, sacks and a failed fourth-down conversion.

Prescott struggled mightily against Indianapolis' two-deep zone coverage, failing to take advantage of the soft spots between zones. Indianapolis was going to force Prescott to dink-and-dunk his way down the field, forcing the Cowboys' offense to nibble its way downfield.

When Prescott tried to take bigger bites with deeper passes to move the offense down the field, he failed, as tight coverage and poorly thrown balls robbed Dallas of its ability to stretch the field.

With the Cowboys unable to get anything going deep, the Indianapolis secondary was able to sit on the wide receivers' stop and breaking routes, giving Prescott minuscule passing windows to his outside weapons. When the receivers were able to generate some separation, Prescott struggled to accurately place his throws, forcing them to make much tougher grabs than need be.

Elliott, on the other hand, had an admirable performance, limping his way to 127 total yards on 26 opportunities. Despite running behind an interior line that consisted of Adam Redmond, Joe Looney and Connor Williams for most of the game, Elliott was able to take advantage of Indianapolis' stacked boxes, averaging 4.83 yards per

behind Dallas' rag-tag line. Still, Dallas' inferior interior O-line put a cap on Elliott's effectiveness, as it limited the offense's ability to fully take advantage of the favorable running situations. Elliott performed well given his health and blockers, but it could have been more -- and likely would have, if Dallas were healthy up front.

Overall, Matt Eberflus' defense was able to shut out the Dallas offense, limiting it to just 292 total yards. This was not the first time we've seen the Cowboys' offense struggle, as it's been one of the bittersweet trends of their season. However, it may have provided the blueprint that if a defense can take away Dallas' outside receiver schematically, Prescott will struggle to adjust, and the offense will sputter when Elliott can't single-handedly will the offense down the field.

Either the Cowboys' offense must do a better job of moving Cooper and Michael Gallup around the formation to create mismatches for the defense -- similar to how Indianapolis was able to scheme T.Y. Hilton into one-on-one matchups with Dallas linebackers on multiple occasions -- or Prescott must be more accurate while the other passing weapons must do a better job taking advantage of their matchups.

Defenses are starting to figure out how to slow down the Cowboys offense with Cooper in the fold. Outside of the fourth quarter and overtime against the Eagles, the Cowboys have scored just nine points in the other seven quarters over the past two weeks.

It's time for the Cowboys' offense to make some adjustments. Their hopes of making a playoff run depend on it.

Running between tackles from condensed formationin short-yardage situation bites Dallas again

When the Cowboys needed a yard to get a first down from inside the Colts 5-yard line, offensive coordinator Scott Linehan made the questionable decision to pull as many players into the box as possible with a condensed formation, choosing to run the ball up front the exact area where the most bodies are located. Here's that play:

Here, the Cowboys are in a single-back set using 13 personnel (one running back, three tight ends, one receiver) with all three tight ends lined up on the right side of the formation. The Cowboys are attempting to run a weak-side zone concept behind Tyron Smith, however, Colts defensive lineman Margus Hunt had other thoughts, quickly beating Looney to stop the play before it could even get started. Even if Hunt didn't get there, it probably wouldn't have mattered, as Indianapolis had plenty of bodies in the area to stop Elliott short of the sticks.

Running the ball into the most crowded part of the field gives the offense no room for error, as missed blocked are amplified due to the numbers of bodies in the area. Moreover, with more bodies near the line of scrimmage and less available space, it speeds up the timing of the blocks.

For example, on a typical zone run, the uncovered interior offensive lineman will have enough time to double-team the defensive tackle before climbing to the second level to block a linebacker, meaning that if the covered offensive lineman gets beat quickly, the uncovered offensive lineman is there to help. However, with every offensive lineman covered in short-yardage situations where the offense is in a condensed formation, there is no available help, as every offensive lineman is immediately engaged with his own man.

If the offense opted to open up the formation, it would have taken defenders out of the box, creating space and giving the offensive line more room for error.

On top of taking defenders out of the box, using a less condensed formation gives Dallas many more options from a play-calling perspective, as it's tough to run RPOs and zone reads from under center with a condensed formation. Dallas would be wise to use more shotgun and pistol formations, making Prescott just as big a threat in the running game as Elliott.

At this point, it may not be wise to get one's hopes up though, as Linehan and head coach Jason Garrett have proven to be fond of the condensed formations in short-yardage situations throughout their tenure, and it will invariably continue to limit the effectiveness of Dallas' short-yardage offense, despite possessing two of the best short-yardage weapons in the NFL in Prescott and Elliott.

Cowboys DTs and LBs have worstperformance of the season

The Cowboys' defense performed poorly Sunday, as the Colts were able to move the ball without resistance for most of the game. Out of Indianapolis' eight possessions, five ended with points and another ended the game, meaning the Colts were successful on 75 percent of their drives -- a recipe for disaster for any team.

Indianapolis' quick passing attack rendered Dallas' pass rush meaningless while poor angles and tackling from the linebackers allowed Indianapolis' short passes to go for intermediate gains throughout the game.

The Cowboys were even worse against the run, as its No. 3 rushing defense -- which had allowed, on average, 86.8 yards rushing per game prior to Sunday -- allowed 179 rushing yards on 39 carries (4.56 yards per carry) to the Colts' rushing attack, which ranked 24th coming into Sunday, averaging 102.5 rushing yards per game.

Most of the blame for Dallas' struggles against the run can go to its defensive tackles and linebackers.

For some reason, when Sean Lee is active, Leighton Vander Esch performs below standard. Prior to Sunday, Vander Esch's two worst performances came against Washington in Week 7 and Tennessee in Week 9 -- Lee was active in both contests.

Fast forward to Sunday, and Vander Esch had another forgettable performance while Lee was active. Vander Esch finished with eight total tackles, but he was slow to diagnose, easily fooled by play-action, bad in coverage and struggled to get off blocks. Though he didn't receive much help, Vander Esch had an uncharacteristically poor performance.

Unfortunately for Dallas, the rest of the front seven performed similarly, as the defensive line failed to get off blocks, making it easy for the Indianapolis ball carriers to get to the second level of the Cowboys' defense, while Jaylon Smith struggled to quickly diagnose Indianapolis' run concepts.

On top of struggling to get off blocks, the defensive tackles were flat-out getting dominated at the point of attack, as they were routinely displaced out of their gap. Mack's third-quarter touchdown run was a great example:

On this play, the Colts are in a single-back, shotgun formation with 11 personnel against Dallas' nickel defense. Indianapolis runs a "wham" concept, where the tight end comes across the formation to wham the initially unblocked Randy Gregory to open a running lane into the end zone for Mack. The key to this play for the Colts was the left guard's block on Daniel Ross, as the Dallas defensive tackle was pinned inside, giving Mack a giant running lane to the end zone.

Because Ross was pinned so far outside, it made Smith appear as though he took too wide of an angle to the hole. However, if Ross is able to hold his ground at the point of attack, Smith would have been in perfect position to bring down Mack at the line of scrimmage.

On top of that, Dallas' defensive tackles didn't demand many double teams, allowing Indianapolis' guards to combo up to the linebackers at the second level without much resistance. Because Indianapolis' interior offensive line was able

to the second level quickly, it ruined Vander Esch and Smith's angles to the ball carrier throughout the game. Vander Esch and Smith are at their best when they can use their athleticism to outpace interior offensive linemen to hole, but that is almost impossible to do if the guards are able to get to the second level without first having to secure the defensive tackle.

Furthermore, on a day when the defense needed Herculean efforts from its defensive ends to compensate for the defensive tackles' struggles, DeMarcus Lawrence, Tyrone Crawford

Gregory were painfully quiet, as the Colts did an excellent job taking Dallas' defensive ends out of the game in the run and pass games.

It was a disappointing performance in what has been a fantastic season for the Cowboys' front seven. Hopefully, for the Cowboy's sake, this performance will end up as an abnormality instead of a sign of things to come.

Twitter: @JohnOwning