ASHBURN, Va. — When the Washington Redskins turned over almost half their starting defense from last season, coach Jay Gruden didn’t know how it would go.

“You’re never quite sure until they get here,” Gruden said.

The Redskins’ defensive newcomers are here, and so far they’re spectacular.

After adding safety D.J. Swearinger, linebacker Zach Brown and defensive linemen Stacy McGee and Terrell McClain in free agency, drafting lineman Jonathan Allen, linebacker Ryan Anderson, safety Montae Nicholson and cornerback Fabian Moreau and welcoming linebacker Junior Galette back from injury, Washington’s defense is ranked fifth in the NFL going into a Week 4 showdown at the undefeated Kansas City Chiefs on Monday night.

Gruden said the improved defensive performance has a lot to do with the Redskins upgrading their talent on that side of the ball.

“When you talk about why we’re better, we have better players,” Gruden said. “Guys are buying in, but most importantly they’re playing hard, they’re playing fast and they’re playing physical.”

It has only been three games, but after allowing almost 378 yards a game last season as the fourth-worst team in the league, the Redskins are surrendering 272 a game. Opponents’ 62.3 yards a game on the ground are the second-fewest in the league.

“That’s the identity as a great defense,” Swearinger said. “You’ve got to stop the run, first and foremost, and make teams one-dimensional and that’s what we’re going to try to continue to do.”

Kansas City’s Kareem Hunt, who’s averaging 8.5 yards a carry and has four rushing touchdowns, is the next challenge for this defense, which is dealing with a hamstring injury to Swearinger and shoulder injuries to Allen and linebacker Mason Foster. Of course Washington has already dealt with missing pieces on defense after second-year safety Su’a Cravens left the team to contemplate retirement and Foster missed its Week 3 game against Oakland.

Defensive coordinator Greg Manusky has been able to mix and match all over as the unit has coalesced earlier than expected. Playing the high-octane Raiders so early had a silver lining.

“With the perfect preparation, anything can happen,” Swearinger said. “I think with the stakes, with us having to play a big game so early, I think it was mandatory that it came early.”

Gruden hoped Allen, a first-round pick, would be able to contribute right away, though Moreau (third round) and Nicholson (fourth) have exceeded expectations. Second-year defensive lineman Matt Ioannidis, a 2016 fifth-round pick, has also made impressive strides.

The Redskins’ free-agent signings have also delivered, and Gruden thinks there’s a common theme.

“The good thing is that they all played,” Gruden said about McGee, McClain, Brown and Swearinger. “Those guys aren’t like they are brand-new guys who haven’t played a lot of football. These guys have played a lot of football. It is just a matter of getting together with the terminology and playing well with your teammates. What drew us to those guys was their work ethic, how hard they played. They all seemed like smart guys, and they fit in well.”

Brown, who made the Pro Bowl last year with the Buffalo Bills, has been as advertised as a fundamentally sound tackler and has the second-most tackles in the league. Cornerback Josh Norman said Brown reminds him of Carolina Panthers linebacker Luke Kuechly.

“ZB, he’s an awesome guy in the middle,” Norman said. “It makes a world of difference if you’ve got a linebacker.”

Making as big an impact as Brown is Swearinger, who quickly became the emotional leader of the defense and the entire team, assuming the role of giving pre-practice speeches in the huddle and serving as a captain. Swearinger is part of the upgraded safety play that has made a substantial difference for the Redskins.