The Buffalo Bills ruined their chances at an undefeated regular season on Sunday Night Football. Buffalo dropped a close game against New England, losing 23-20 against their division rivals. New England deserves a lot of credit for marching into Buffalo and earning a signature win against on the best teams in the NFL. That should not get lost in this conversation.

However, from Buffalo's perspective, it must feel like a disaster to drop a home game against a division rival. Especially when considering Buffalo's opponents in the AFC East.

Bills head coach Sean McDermott will admit that his team did not play up to their standard on Sunday Night Football.

“We didn't play our game tonight, and that's frustrating,” McDermott said after the game, per ESPN's Alaina Getzenberg. “And this is a pivotal learning opportunity for us right here. So, there were some other moments where I just feel like maybe we were too cute at times. And just overall, we've got to look at some things and just be honest with ourselves and learn from it holistically.”

It certainly is not time to panic for the Bills, at least not yet. But Buffalos needs to take a long hard look at the film and figure out what went wrong.

So who is most responsible for Buffalo's Week 5 loss? Were these one-off issues, or do they point to some systemic problems with the Bills?

Below we will explore which Bills are most to blame for Sunday's ugly loss against the Patriots.

James Cook, running game thoroughly snuffed out

Buffalo Bills running back James Cook (4) runs against the Miami Dolphins in the second half at Highmark Stadium.
Mandatory Credit: Gregory Fisher-Imagn Images

The Bills would have loved to have ran all over the Patriots. That's often when great NFL teams can pull away from the competition.

Unfortunately, all of Buffalo's rushers not named Josh Allen struggled against the Patriots.

Bills running back James Cook was the worst of the bunch. He only turned his 15 carries into 49 yards, which is only good for 3.3 yards per carry. Failing to surpass 50 yards, especially on so many attempts, shows that New England had his number for the entire game.

Buffalo's lack of balance on offense contributed to their loss, but it was not the worst part of the game either.

Regardless, Buffalo needs Cook to play at a high level if they want to remain one of the NFL's best teams. He rumbled for over 100 rushing yards and at least a touchdown in three consecutive games before Week 5.

Bills fans will be looking for Cook to bounce back in Week 6.

Penalties, turnovers were too much for Bills to overcome

Sadly, the Bills were their own worst enemy on Sunday Night Football.

Buffalo lost largely because of their multitude of self-inflicted errors, including several penalties and too many turnovers.

“Not going to win a football game turning the ball over three times in our red zone,” Allen said. “Gave them one in their red zone. That's just bad football, and we just did not play good tonight.”

Buffalo's first fumble happened on a botched handoff between Allen and tight end Dawson Knox. Bills receiver Keon Coleman also fumbled the ball after catching a pass. This turnover was particularly costly because it set the Patriots up just 11 yards from the end zone.

Finally, Josh Allen himself threw an interception in the red zone during the third quarter. It was only his second interception of the season, but it came at the worst imaginable time.

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“We shouldn't have even been in it with three turnovers,” Allen said. “So, again, that's just … piss-poor offense.”

The Bills also committed 11 penalties for 90 yards throughout the game.

Ultimately turnovers can be streaky in the NFL. And the Bills were riding a 26-game streak of not losing the turnover battle with their opponents.

Buffalo should recover from this fluky game. But fans may want to start paying attention if the same issues pop up against in Week 6.

Buffalo could not stop Stefon Diggs in epic revenge game

New England Patriots quarterback Drake Maye (10) and wide receiver Stefon Diggs (8) walks off the field against the Buffalo Bills after the game at Highmark Stadium.
Gregory Fisher-Imagn Images

The Bills did not play good enough pass defense to beat the Patriots.

On paper, there's no reason why Buffalo should have given up 10 receptions and 146 yards to Stefon Diggs. But that's where the personal element of football comes into play.

Diggs willed himself to have a strong performance in what amounted to a revenge game against the Bills.

“When it gets loud, it kind of gets quiet for me,” Diggs said. “It doesn't bother me too much: They love you one day, they hate you the next, they can love you again. I spent a lot of time here. I respect the dynamic. Used to be here. I'm not here no more. I guess I miss you too.”

The Bills famously traded Diggs to the Texans during the 2024 offseason. But Diggs got his revenge with the Patriots on Sunday.

Buffalo does appear to be missing Matt Milano and Maxwell Hairston, as both players could improve the coverage unit.

Personally I have not seen enough yet to panic about the Bills' defense. But I will be keeping my eyes peeled for how they perform against the Chiefs and Buccaneers in November.

That will provide a more appropriate test for how Buffalo's defense is holding up approaching the playoffs.