In August, the idea of the Patriots putting together another undefeated regular season—a rare feat they accomplished in 2007—was not completely ridiculous to imagine. (Right? Right, guys?) We’d all watched the defending Super Bowl champs work the trade phones and maneuver deftly through free agency, building what looked like the franchise’s deepest, most talented, and most complete team yet. Bill Belichick and Co. added a few new pieces to an already stacked offense (receiver Brandin Cooks, running backs Mike Gillislee and Rex Burkhead, and tight end Dwayne Allen, among others), and acquired a handful of important pieces (like big-ticket free-agent cornerback Stephon Gilmore) to a defense that had given up the fewest points of any team in 2016. A 16-0 season was always going to be a long shot—the NFL season is long and a lot of wild things can happen—but the dream of the Patriots running the table died an early death when they lost their opener to the Chiefs in Foxborough.

New England lost again at home three weeks later when the Pats’ reeling defense allowed 33 points and a game-winning drive to Cam Newton and the Panthers, squandering Tom Brady’s late-game heroics. At that point in the season, it was fair to start to question if another Super Bowl run was in the cards. Was the future Hall of Famer’s brilliant play going to be good enough to overcome what had suddenly become the worst defense in the NFL? Through four weeks, New England was 2-2 and had surrendered 32 points per game (second worst) and a league-worst 1,827 scrimmage yards, nearly 300 more than the next-worst defense in the league (Indianapolis). The Pats had given up a league-worst 1,296 pass yards, were tied for a league-worst 11 touchdown passes allowed, were giving up a second-worst 5.1 yards per carry, and had surrendered 531 total rush yards (27th). The defense was beyond terrible. Put it this way: Early in the year, if anyone on your fantasy team was going up against the Patriots, you were starting that guy and probably getting double-digit points out of him.

Fast-forward nine weeks and the early-season concern that an uncharacteristic, historically bad Patriots defense would foil New England’s shot at its sixth championship has been quashed. The Patriots have won eight in a row, and, in that stretch, the defense has given up just 11.8 points per game—best of any team in the league. New England’s allowed just eight pass touchdowns (tied for sixth best) in those eight wins and held opposing passers to a 75.4 passer rating (seventh). And after a 23-3 blowout win over the Bills on Sunday, the team has climbed all the way up to ninth on the list for points allowed per game (18.6).

The Patriots’ defensive turnaround hasn’t been the result of major scheme overhauls or the infusion of any big-time playmakers. Instead, incremental improvements in every area across the board have helped that unit transform into something respectable. No one’s going to confuse this group with the Ravens’ or Jaguars’ star-studded defenses—and they still rank just 29th in Football Outsiders’ DVOA, something that FO editor Aaron Schatz has discussed in detail here—but compared with the unit we watched early in the year, this group is more disciplined, communicates better, and has simply gotten cleaner performances from its most important role players. These guys are—as the Patriots’ old, cliché motto goes—doing their jobs.

What’s remarkable is that New England has made that improvement despite major losses to injury. Star linebacker Dont’a Hightower, who went on the injured reserve in November with a torn pectoral, has been replaced admirably by Kyle Van Noy—not an easy task considering Hightower was a hybrid linebacker–pass rusher in the Patriots’ scheme. When Van Noy left Sunday’s game against the Bills with a leg injury, Elandon Roberts and veteran David Harris took over without any noticeable hiccups. And when pass rusher Trey Flowers missed last week’s game with a rib injury, he was replaced by Eric Lee, a recent pickup from the Bills’ practice squad. Lee notched four tackles, 1.5 sacks, three quarterback hits, an interception, and two passes defended in his second game with the team.

That victory over Buffalo was, in some ways, a microcosm of how the defense has evolved: It still frequently gives up yards in chunks but has better success keeping opponents out of the end zone. Despite that 11.8-point-per-game average over the last eight weeks, the Patriots are 15th in total yards surrendered (2,681), 12th in passing yards (1,673), and 12th in rush yards given up (918) in that frame. Against Buffalo, New England surrendered 185 yards on the ground—well above its season-long average—but kept the Bills out of the red zone for most of the day and tightened once Buffalo got there, allowing just one field goal on two of the Bills’ trips inside the 20-yard line. The Patriots have made their money over the past nine weeks in that area, and in that stretch they’ve been the third-best defensive red zone in the NFL. On the year, New England’s given up a touchdown on just 45 percent of its opponents’ red zone trips—seventh best leaguewide.

The Patriots’ defensive backs have sorted out the communication and assignment problems from earlier in the year and have mostly played like a harmonious unit in recent weeks. Safeties Duron Harmon and Devin McCourty have provided reliable play in the middle of the field, as has Patrick Chung, who has operated as the team’s defensive Swiss army knife by playing a little bit of everywhere in the secondary. Cornerback Malcolm Butler has shaken off a rocky start to provide some of his trademark playmaking ability as the year’s gone on. In Butler’s first four weeks, he allowed 16 catches on 19 targets for 134 yards, two touchdowns, and one pick in coverage, good for a 109.2 passer rating against (87th leaguewide), per Pro Football Focus. Over the past eight games, he’s given up 25 catches on 52 targets for 406 yards, three scores, and one interception in coverage, registering a more respectable 85.9 rating against (43rd). Stephon Gilmore’s improvement in that stretch has been a major factor for the defense’s overall jump forward, too. During the team’s first four games, he surrendered nine catches on 13 targets for 151 yards, one touchdown, and one pick for a 101.8 passer rating against (74th). In his five games since (he missed weeks 6-8 with a concussion and ankle injury), he’s given up just 18 catches for 164 yards, one touchdown, and one pick for a 67.7 rating—15th best.

Gilmore’s development as the team’s shutdown corner—the role they envisioned when they gave him a five-year, $65 million contract in the spring—was apparent Sunday when he gave up just two catches on eight targets for 22 yards to go along with two pass breakups against his former team. The Bills tried to target their old teammate deep in the red zone late in the game, testing him on three separate end zone throws, and Gilmore responded by shutting them down.

The Patriots defense benefits from playing with one of the league’s top offenses and a very good special teams group. They’re going to be on the field less and see excellent field position—factors that skew the team’s points-per-game statistic in their favor. So, despite such a stark improvement in that metric, no one’s going to go so far as to say this is a defense that’s suddenly transformed into a world-destroyer; it’s just turned into a moderately good one—and that might be enough. New England doesn’t need its defense to be the most efficient unit in the NFL to win its second straight Super Bowl. With Brady at the helm, an average defense could be good enough to make the Patriots the clear AFC favorites.

The team’s defensive metamorphosis is not yet complete. New England must keep things on track against the Dolphins, Steelers, Bills, and Jets in the last month of the season, but the change we’ve seen is incredible nonetheless. There’s a two-week overlap here, but consider this: The Patriots have transformed from the first team in NFL history to allow a 300-yard passer in six straight games to the first group in Belichick’s tenure in New England to hold eight straight opponents to under 20 points.

Early in the year, it seemed that for the Patriots and their league-worst defense to make any postseason noise, they’d need a 40-year-old Brady to drag them along, scoring 35 points a game—with little margin for error. But now that the defense is pulling its weight and shutting teams down in the red zone, it means Brady can have an off day, like he did against the Bills on Sunday (he took three sacks and passed for just 258 yards, no touchdowns, and one interception), and they’re still capable of producing a blowout. That balance makes the Patriots hard to beat, and it makes them pretty damn scary as we inch closer to the playoffs.