Well, that was a disaster. The New England Patriots suffered one of the worst, if not the worst, loss of Bill Belichick's 24-year tenure on Sunday, falling to the Dallas Cowboys, 38-3. The 35-point loss is the largest defeat Belichick has suffered in his 29 seasons as a head coach, further cementing the magnitude of Sunday's loss.

Here are the five things most to blame for the downright no good, very bad and ugly loss.

5. Mac Jones

The Patriots quarterback had the worst game of his life on Sunday. So bad that you look at his stat line of completing 12 of 21 passes for 150 yards with two interceptions and think, “How wasn't it worse?”

Things unraveled for Jones quickly. He lost a fumble that led to a scoop-and-score on the second play of the Patriots' third drive. After a three-and-out on the next drive, Jones threw an interception on a pass across the field, easily allowing DaRon Bland to scamper 54 yards into the end zone. Jones nearly threw another interception as he ran into pressure on the next drive. He threw an interception on the first drive of the second half, and badly overthrew DeVante Parker on a third-down pass over the middle in the ensuing possession–a three-and-out that ended his day.

Jones never gave his team a shot to win on Sunday. What's even more disappointing is that he appeared to show progress from last season through the first three games. Sure, it wasn't perfect but he at least helped his team work their way back into games against the Philadelphia Eagles and Miami Dolphins.

Sunday's performance almost erases that. Or at least it feels like it does. Now, those questions on if he's the guy long-term for New England turn into doubts for many.

Who could blame them? Jones' situation around him is probably close to the worst in the league for any quarterback over the last two years. But he was sold as a quarterback that would at least keep things steady. He's fulfilled that promise, at times. But he's also failed to consistently deliver in moments when he's been asked. And if he continues to have stinkers like he did on Sunday, then there's no purpose of playing him at quarterback anymore.

4. Michael Onwenu

Speaking of another guy that put his team behind the eight-ball on Sunday, the Patriots right guard might have had the worst game of his NFL career, too.

Michael Onwenu had three penalties that put the Patriots in bad spots each time, with one of them arguably killing a drive early in the second quarter. He and Vederian Lowe were also lit up on the right side of the defensive line all afternoon, struggling to contain Dallas' mighty pass rush.

3. Rhamondre Stevenson

What's up with Stevenson?

The Patriots running back had another struggling performance on Sunday. He rushed for 30 yards on just 2.1 yards per carry, bringing his season average to 2.7 yards per carry. The protection wasn't great upfront, making things a bit more difficult for the running back. But he looked like he wasn't seeing lanes either, at least not at the level that Ezekiel Elliott did on Sunday. It's not really a surprise that the offense has cratered to the level that it has considering their top player from last year has just been bad so far.

2. The Patriots' secondary

Christian Gonzalez's injury on the Cowboys' second drive of the game meant that the Patriots were playing without their top four corners on Sunday.

That certainly looked to be the case.

Dak Prescott didn't have much difficulty passing the ball, completing 28 of 34 passes for 261 yards and a touchdown. Obviously, missing Gonzalez and your other three top corners stings. And it isn't necessarily fair to pin blame on backups. But CeeDee Lamb only had four receptions for 36 yards and Dallas' other receiving options aren't great. Rookie tight end Jake Ferguson was the game's leading receiving with seven receptions for 77 yards. Michael Gallup had five for 60. Jalen Tolbert had four for 53.

You get the point. It wasn't any one receiver that was gashing the Patriots' secondary on Sunday. It was a mix, and New England's secondary looked confused pre-snap on multiple occasions, with players guessing on their assignments.

1. Bill Belichick

Sunday's loss was maybe the most telling of Belichick's roster-building approach following Tom Brady's departure.

The quarterback was horrific. But his team certainly didn't make things easier for him, either. The Cowboys' front seven seemed to own the Patriots' offensive line for much of the afternoon. The receivers weren't really creating separation on many instances, which was evident on Jones' second interception as he forced a fourth-down pass to JuJu Smith-Schuster. Demario Douglas had a 42-yard reception on New England's opening drive and was nowhere to be seen for quite some time after.

On the other side of the ball, Dallas' offense had its way with New England before it reached the red zone. It got the ball within New England's 25-yard line on six of its eight possessions in Sunday's game (excluding end of half drives) as its skill position players made plays all over the field.

In addition, Belichick also left his starters (outside of Jones) in the game for way too long, playing them well into the fourth quarter. That decision might have cost them their best player for the rest of the season as Matthew Judon suffered an elbow injury late that reportedly seems serious.

Just bad, bad, bad.