Buffalo Bills head coach Sean McDermott works on the sideline during a preseason game against the Chicago Bears in Chicago. AP Photo

ORCHARD PARK — The NFL schedule had not yet been released last spring when Buffalo Bills coach Sean McDermott already decided he was taking on the extra duties as defensive coordinator.

With the Bills’ season opener at the New York Jets on Monday night fast approaching, McDermott wasn’t second-guessing his decision, while knowing his first test comes against a retooled Aaron Rodgers-led offense.

“Well, they’re not easing me in, that’s for sure,” he said Wednesday.

Don’t be fooled.

Challenging as it might be to face one of the NFL’s most accomplished quarterbacks, and taxing as the additional duties have been on his schedule, the former Eagles and Panthers defensive coordinator feels reinvigorated at the opportunity to return to his coaching roots.

McDermott’s decision to take on more is less about filling a void on his staff in February, after announcing Leslie Frazier was taking the year off from coaching.

Instead, this fills a hole McDermott felt was missing in what became an it’s-lonely-at-the-top revelational moment seven years after arriving in Buffalo as a first-time head coach.

“The head coach’s seat is a leadership seat and that’s all good, and I love that part of it,” McDermott said.

“But what you miss the most is rolling up your sleeves and getting in with the players side by side.”

McDermott’s more hands-on approach has been notable among players on both sides of the ball.

“It’s a different dynamic for sure,” defensive tackle Jordan Phillips said.

“Guys like it. When he says he puts on his head coaching hat and his DC hat, there’s a difference. You can actually see it,” Phillips added. “I’m not going to get into any details, but he’s a little more colorful when he’s in the defensive room.”

Quarterback Josh Allen began sensing McDermott’s influence on the defense during spring practices.

“It’s getting competitive out there, you know, a little trash-talking back and forth with coach,” Allen said. “It’s fun to see his competitive juices get flowing. He’s a defensive guy, so that defense is always a special part of him, but I think even more so right now.”

How that translates on the field remains to be seen. And yet the defense in practice and preseason games showed more of an attacking style — an element that at times appeared to be missing under Frazier’s six-year watch.

Though Buffalo’s defense has statistically ranked among the NFL’s best in numerous categories over the past five years, the unit was also known for experiencing several memorable letdowns in key moments.

The most notable happened two seasons ago in a 42-36 overtime loss at Kansas City, an AFC divisional playoff game now dubbed “13 Seconds.”

That’s how much time was left on the clock in regulation when the Chiefs gained 44 yards on two plays to set up Harrison Butker’s game-tying 49-yard field goal, before securing the win with an overtime-opening eight-play, 75-yard touchdown drive.

The Bills defense also sagged in closing last season with a 27-10 loss to Cincinnati in the AFC divisional round. Cincinnati scored on its first two drives and eventually rolled up 412 yards against an injury-depleted defense, and the team still dealing with the lingering emotional effects of safety Damar Hamlin’s near-death experience three weeks earlier.

The Bills have not entirely made clear the reasons behind Frazier’s decision to take the year off, while still under contract. Frazier, 64, also has not shed much light on his decision other than to say he wanted to spend the year pursuing head coaching opportunities after failing to land even an interview last offseason.

Frazier was McDermott’s first hire in Buffalo, and regarded as a trusted confidante in eventually being promoted to assistant head coach.

In his new dual role, McDermott is leaning on his defensive staff for help and input. It’s a group that includes several former coordinators as well as assistants who worked under McDermott in Carolina, including defensive line coach Eric Washington, who has taken over the assistant head coach’s title.

“Being in a situation where he can communicate directly to the defense and the staff, and just kind of be hands-on, that’s where he started,” Washington said of McDermott. “That’s where his love is. That’s where his passion is.”

McDermott believes his defensive approach has evolved from benefitting from his head coaching duties, and becoming more familiar with offensive strategies.

“When you’re just strictly on one side of the ball, you don’t get a chance to get exposed to that knowledge, to that wisdom. And it helps you when you cross-train a little bit,” he said.

What’s not changed is McDermott placing an emphasis on winning at the line of scrimmage and pressuring opposing quarterbacks. Being aggressive is what led to McDermott going undefeated in 75 straight matches in becoming a two-time national high school wrestling champion, and had him pegged as a potential coaching candidate while playing safety at William & Mary.

It’s a personality McDermott hopes rubs off on his defense.

“I want them to be themselves, but at the same time understand that they’re taking on a certain personality. Yes, mine, but also everyone’s personality combined in that room, including the staff,” he said.

McDermott smiled, in letting his guard down, when asked to describe his personality.

“I think you know me well enough,” he said.