Sean McDermott certainly could have done without three turnovers, nine penalties, and several special teams gaffes, but if his Buffalo Bills can run the ball and play defense the way they did Saturday afternoon, the coach would be a happy man.

McDermott has given his blessing to a wide-open passing offense led by Josh Allen, first coordinated by Brian Daboll and now Ken Dorsey, but you know McDermott: He’s an old-school defensive guy and he still believes that running the ball and playing great defense are vitally important to the pursuit of a championship, and the Bills did both of those things very well in their 35-13 victory over the Chicago Bears.

“First half wasn’t pretty,” McDermott said. “Penalties, turnovers, field position. I think that really dictated the flow a lot the first half. Second half, we cleaned some things up.”

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Did they ever. The Bills overcame a 10-6 halftime deficit by scoring four touchdowns in the last two quarters and the key was the run game which produced 160 of its 254 total yards, and the defense which forced a key turnover early in the third and permitted just one Bears field goal.

“Yeah, we played better complementary football,” McDermott said. “And it really all started by the offense coming out and getting into a rhythm, executing at a higher level than we were in the first half. And then Dane Jackson got the takeaway (a forced fumble recovered by Tim Settle). So that was good to see.”

Here’s how I graded the Bills’ performance:

PASS OFFENSE: C-

It was a brutally cold day, the kind of day where it’s extremely difficult to be efficient and error free on offense. That said, this was not a performance Josh Allen will look back fondly on. He completed 15 of 26 passes for 172 yards and two TDs, but also threw two bad interceptions and could have had a couple others.

What was so puzzling is the complete inability to get Stefon Diggs involved against two young cornerbacks who should have been taken advantage of. Diggs was targeted just twice and caught both for 26 yards, continuing a downward trend for him. The Bills have to start getting him back to being dangerous because right now, he’s not.

Gabe Davis caught a TD pass, but he also lost a fumble, failed to get both feet in bounds on a catch, and then sort of gave up on a third-down pass to the end zone where, had he kept going, might have drawn a pass interference penalty. I continue to say he’s been one of the Bills most disappointing players this season.

Up front, the Bills’ line protected Allen well, though they were going against one of the least effective pass rush teams in the NFL. Still, it was a good job as Allen was sacked only once and hit two other times.

RUN OFFENSE: A+

The Bears could not stop the Bills on the ground. Devin Singletary gained 106 yards, his first 100-yard game of the season, and James Cook nearly had his first career 100-yard game, falling just short at 99. Each scored a lengthy TD and combined, they averaged 8.9 yards per carry. It was hugely impressive.

When you add in Allen’s 41 yards, the Bills finished with a season-high total of 254 and averaged 8.2 per attempt. Credit to the offensive line, which I have bashed repeatedly this season. But this was an impressive performance as they played without center Mitch Morse, then lost his replacement, Ryan Bates, for a short period meaning Ike Boettger made his season debut.

When the Bills needed to get control of the game, it was Singletary’s 33-yard TD and Cook’s 27-yarder less than three minutes apart in the third quarter that did the trick.

PASS DEFENSE: A

The Bills limited Justin Fields to 119 passing yards and a touchdown. Outside of a 44-yard completion to Velus Jones at the end of the third quarter, Fields was anemic through the air, but that was to be expected as the Bears have the worst passing attack in the NFL. His next-longest completion was a 20-yarder to Byron Pringle.

The pass rush did a great job of setting the edge and forcing Fields to stay put and that’s not where he’s at hist best. Ed Oliver and A.J. Epenesa recorded sacks and Oliver also batted down two passes. Matt Milano and Tre’Davious White also had pass breakups, and JaQuan Johnson intercepted a Nathan Peterman Hail Mary on the final play of the game.

RUN DEFENSE: A-

After a terrible first drive when the Bears rushed for 43 yards on their way to the end zone, they managed only 37 the rest of the way. Chicago came into the day No. 1 in the NFL in rushing at 186 yards per game, but finished with just 80, and 2.8 yards per carry.

David Montgomery looked like he was going to have a big day when he broke a 28-yarder early but he finished with 62. And Fields was a shocking nonfactor. He ran seven times for 11 yards, easily his worst rushing game of the season in a year when he’s got over 1,000 yards.

LBs Tremaine Edmunds (nine tackles) and Milano each played a big role in that as they did an excellent job in Buffalo’s zone defense, covering their area but also keeping their eyes on Fields when he dropped back to pass and being ready to move when he tucked it away. Damar Hamlin had six tackles and two of those were for lost yardage. In total, the Bills had 11 tackles for lost yardage.

SPECIAL TEAMS: F

The Bills kickoff coverage team got off to a horrible start and it never got better. Just a terrible day all the way around. Velus Jones returned the first two kickoffs 36 and 40 yards, giving the Bears great field position. For the day, he averaged 28.3 yards on four returns.

Tyler Bass fell victim to the wind as he missed his first extra point and then missed a 38-yard field goal near the end of the first half. He did rally to make his final three extra points.

Nyheim Hines made a terrible decision to let a second-quarter punt hit the ground and it rolled all the way to the 2. In the third quarter he dropped a punt but was able to recover, and he muffed a kickoff in the fourth quarter that resulted in a drive start at the 13.

Siran Neal had a holding penalty on the second-half kickoff that wiped out a nice Hines return and cost the Bills 22 yards in field position, and Tyrel Dodson had a holding penalty that cost the Bills 20 yards. All of this needs to get fixed in a hurry.

Only Sam Martin had a nice game as he averaged a 49.7 net on three punts including a 62-yarder that was downed inside the 20.

COACHING: B+

Fields was the biggest concern for the Bills defense, and Leslie Frazier put together a great plan that completely stymied him. The Bills kept him contained in the pocket and never let him do any damage on the edges, and when he can’t do that, the Bears are helpless. You want to talk about adjustments, the Bills sure made a bunch after that game-opening drive.

On offense, Ken Dorsey made a few puzzling decisions, and they were born out of his complete faith in Allen. On a windy day and with their ground game working so well, it was somewhat baffling how Dorsey continued to ask Allen to pass. However, as Allen said, you can’t sniff at 35 points, 426 yards and 7 of 12 on third and fourth down.

Special teams coach Matthew Smiley has some work to do this week. His units were deplorable all day and against a better team, their mistakes could have been far more costly.

Sal Maiorana can be reached at maiorana@gannett.com. Follow him on Twitter @salmaiorana.To subscribe to Sal's new twice-a-week newsletter, Bills Blast, please follow this link: https://profile.democratandchronicle.com/newsletters/bills-blast

This article originally appeared on Rochester Democrat and Chronicle: Bills report card: Buffalo pounds Bears with ground game and defense