FOXBOROUGH, Mass. — First-year inside linebackers coach Jerod Mayo has taken a leading role on the New England Patriots‘ defensive staff, helping to fill the void created when Greg Schiano resigned in March, but there’s still no question who is ultimately in charge of the NFL’s No. 1-ranked unit.

“We have the benefit of having Coach Belichick in the room with us each and every day,” Mayo said, noting that Bill Belichick’s presence is critical, “especially having a young coaching staff.”

Belichick’s defensive acumen is well-documented, with his Super Bowl XXV game plan as New York Giants defensive coordinator having its own place in the Pro Football Hall of Fame.

That expertise has helped soften the blow of a situation that might have crippled another team. When 2018 defensive playcaller Brian Flores left to become coach of the Miami Dolphins in the offseason, and then Schiano unexpectedly stepped down, Belichick acknowledged he would have more oversight on defense this season.

The results, albeit against struggling teams — the Pittsburgh Steelers, Dolphins and New York Jets are all winless — have been sizzling.

According to Elias research, the Patriots are the only team since 1945 not to allow a touchdown from the line of scrimmage through their first three games.

The three points allowed by their defense are by far the fewest through three games in the Super Bowl era (the previous mark was 12, most recently by the 2004 Seattle Seahawks).

And opponents have a 12.8% conversion rate on third down, which is the lowest allowed through three games by any defense in the past 40 seasons, according to Elias data.

The Patriots will be tested Sunday on the road against the 3-0 Buffalo Bills (1 p.m. ET, CBS), but so much for the thought that the 67-year-old Belichick, who lost three assistants on defense from the 2018 staff, might find himself spread too thin.

“We have a lot of good coaches on our staff. I have a lot of confidence in them. They do a great job, they work hard, they’re well prepared,” Belichick said this week. “I’d say the interactions are something that we’ve grown through in the offseason and training camp. It’s gone well.”

Belichick’s expanded oversight on defense is a topic he has been reluctant to expound upon this season, right there alongside injuries. He also seemed to previously instruct coaches not to get into detail about it.

But those familiar with what is unfolding on game day say Belichick is in charge of calling the defense, with Mayo helping relay in the call to players. Safeties coach Steve Belichick also is involved in the communication.

What seems important to all involved is to stress the collaborative nature of contributing to the game plan, with everyone doing their part, which includes former Arkansas coach Bret Bielema (defensive line), DeMarcus Covington (outside linebackers), Joe Kim (director of skill development), Mike Pellegrino (cornerbacks) and coaching assistants Brian Belichick and Bob Fraser.

With no coach officially listed as coordinator, Bill Belichick is closest to it.

“He is the head guy and lets everyone know what it’s all about, who to look for, and give everyone the points they should focus on,” fourth-year defensive end Deatrich Wise Jr. said of Belichick. “He gives the pointers, and the guys go back in there and hit the points — and get really detailed with every point.”

Linebacker Elandon Roberts, one of the team’s captains, offered his take.

“Of course, everybody knows Bill’s involved the whole way with the defense,” Roberts said. “I feel like he’s always been involved heavily in the defense, but he also has a lot to do as a head coach. From the same standpoint, it’s a collective group. We all come together and we all say, ‘Let’s try this, let’s try more of that and see how it works.’ Then come Sunday, we’re able to put it all together.”

Specific to the 33-year-old Mayo, veteran defensive end Michael Bennett joked that it’s unusual having a coach in a top role who is the same age as him.

Defenders also have said that Mayo’s history with the Patriots — from having been a 2008 first-round pick who played through the 2015 season — has added a helpful perspective. That has carried over to the coaching staff, as well.

“His experience as a player in our system is very valuable,” Belichick said. “We can talk about calls that we can make on the field, or identifications and so forth, and his perspective of, ‘Yeah, that’s no problem, that’d be easy for us to do or that’s a lot harder’ — it makes us rethink and have that perspective of how easy it is or isn’t for a player in certain situations.

“He’s done it, and he’s done it under pressure and dealt with a lot of things we currently deal with, and so that’s a good perspective to have in the room. We don’t have that from anybody else defensively.”