49ers' Pass Defense Must Adjust After Being Exposed by Josh Allen, Bills

The San Francisco 49ers went from looking like a potential playoff team to a squad with plenty of flaws in the span of a week. 

Kyle Shanahan's team fell to 5-7 through a 34-24 loss to the Buffalo Bills on Monday that was not as close as the score reflects. 

Robert Saleh's defense struggled to contain the Josh Allen-led passing attack, and few adjustments were made to keep the Bills' stable of wide receivers at bay. 

The San Francisco defense did not receive much help from the offense that looked stagnant at times. The 49ers failed to establish their typical offensive identity on the ground. 

The 49ers are just one game back of the Minnesota Vikings and Arizona Cardinals in the NFC wild-card race, but they looked far from a postseason squad in Monday's defeat.

Lack of Adjustments Allowed Josh Allen to Torch Defense

Ross D. Franklin/Associated Press

Buffalo earned the most total yards and passing yards off San Francisco's defense this season. 

Allen led the Bills offense to 449 total yards, 368 of which came through the air. Cole Beasley and Stefon Diggs combined to catch 19 of Allen's 32 complete passes. 

The Buffalo quarterback picked apart the 49ers secondary through the crisp route running of both players. 

On Beasley's touchdown, he set up on the edge of the goal line to haul in a pass. Diggs' route running was on display all night, with the highlight being a move that left Jason Verrett in the ground. 

The lack of successful adjustments from Saleh's defense was shocking after he turned in a play-calling masterpiece against the Los Angeles Rams in Week 12. 

Instead of adding to that victory and reaching .500, the 49ers have to go back to the film room and dissect how to not get burned by a talented set of wide receivers again.

San Francisco has to figure out its defensive adjustments fast because Week 14's clash with the Washington Football Team is all of a sudden a playoff elimination game between two 5-7 fringe wild-card contenders.

49ers Need More out of Raheem Mostert, Ground Game

John Cordes/Associated Press

While the defense was conceding season-high yardage totals, the offense got away from what makes it so dangerous. 

San Francisco totaled its second-lowest rushing total of the season, as Raheem Mostert and Co. managed 81 rushing yards. 

Mostert and Jeff Wilson Jr. were effective when they were called on, but Shanahan did not go to them on a consistent basis. Mostert had nine carries for 42 yards and Wilson gained 47 yards off seven carries. 

Shanahan may have been more inclined to throw in the second half since the 49ers were playing from behind, but if he stuck with the ground game, the offense could have been more successful. 

Monday's pair of feature backs were effective enough to move the ball down the field, but they were not trusted as much as they usually are. 

Mostert carried the ball 10 or more times in four of his six appearances and Wilson earned 29 touches in the running game in his last two appearances prior to Monday. 

San Francisco does not have to abandon the aerial attack to win games, but it needs to be more balanced moving forward to get the most out of its top offensive strength with Nick Mullens under center. 

Loss Gives 49ers No Margin For Error To Snag Playoff Spot

Rick Scuteri/Associated Press

Monday's loss dropped the 49ers into a four-way tie at 5-7 with the Chicago Bears, Detroit Lions and Washington. 

A strong case could be made that the 49ers are the best team out of that foursome when they are their best, and they will get a chance to prove that in Week 14 versus Washington. 

With four games left in the season, the 49ers can't afford a loss to another contender, so they have to beat Washington to have any chance of making a late playoff push. 

The same thinking can be applied to the Week 16 meeting with the Arizona Cardinals, who are tied at 6-6 with the Minnesota Vikings. 

At minimum, the 49ers have to win those two games to improve its conference record and earn at least one head-to-head tiebreaker. If they win in Week 16, they would split the season series with Arizona. 

The Week 15 meeting with the Dallas Cowboys can be chalked up as a win right now, which means the 49ers could go 3-0 and enter the regular-season finale with the Seattle Seahawks with a playoff spot on the line. 

To even reach that spot, the 49ers need to fix the flaws from the Buffalo loss in the NFL's most unique environment. They are currently practicing and playing home games in Arizona due to restrictions in Santa Clara county.

If the 49ers play a more complete game in Week 14, it could be the start to a late playoff run, but if they fail to improve on Sunday, they likely will not have a chance to defend their NFC title. 

Follow Joe on Twitter, @JTansey90.

Statistics obtained from Pro Football Reference.