Jeffrey T. Barnes/Associated Press
The list of the AFC’s best teams is as follows: 
1. The Kansas City Chiefs
2. The Buffalo Bills 
Buffalo finally earned the right to call itself one of the conference’s elite squads with Sunday’s 26-15 victory over the Pittsburgh Steelers. In doing so, Pittsburgh dropped out of the conversation thanks to a two-game losing streak, while the Bills are the team to challenge the Chiefs for AFC supremacy and possibly knock off the reigning Super Bowl champions during the postseason. 
More importantly, the Bills clearly have a franchise quarterback in place with Josh Allen’s continued outstanding play. With a potential MVP candidate behind center, Buffalo took what looked good on paper this spring and made it a reality. 
After the completion of the Stefon Diggs trade, the following line appeared in Bleacher Report’s reaction column, “The Buffalo Bills are now the AFC East’s team to beat.” 
Even then, the franchise’s path toward success was easy to envision, though much harder to achieve. Buffalo built a well-rounded roster to compete with the NFL’s best. Three stages had to take place for that to occur. 
First, the Bills couldn’t allow the Patriots to be the divisional bully anymore. Second, the squad had to show up against the league’s best competition. Finally, Allen’s development needed to grow dramatically after last season’s performance. 
The initial step might have been easier than initially expected. Sure, the Patriots lost Tom Brady to the Tampa Bay Buccaneers this offseason, but the organization still features the game’s best head coach and seemingly found a bargain in free-agent quarterback Cam Newton. Buffalo’s 24-21 victory over the Patriots in Week 8 set the table. 
Sure, Buffalo won contests against quality opponents like the Los Angeles Rams and Las Vegas Raiders earlier in the season. Then, the team faltered against the Tennessee Titans and Chiefs. But handling business within the division means more, especially when a specific opponent had a stranglehold over the AFC East. New England’s string of 11 straight division titles ended this season due, in part, to Buffalo’s ascension, thus getting a giant gorilla off the franchise’s back. 
Jeffrey T. Barnes/Associated Press
From there, possibilities widened. Victories over the Seattle Seahawks and Steelers, both of whom are considered Super Bowl contenders, showed the Bills are capable of so much more. Buffalo won six of their last seven contests, including all three of their post-bye games. 
Sean McDermott’s squad struggled with some mistakes and miscues Sunday before taking over in the second half, which is no small feat considering the Steelers held the league’s last undefeated record less than two weeks ago. 
The Bills countered an aggressive Pittsburgh defense with quick hitters while taking shots downfield when available. Buffalo’s D, meanwhile, didn’t allow quarterback Ben Roethlisberger to establish a rhythm. The Bills attacked a makeshift offensive front and harassed the now near-immobile veteran. Quick drops and misfires derailed the Steelers’ entire gameplan and Buffalo took advantage of the situation. 
An opportunistic approach really showed who Allen and the Bills can be through the rest of the regular season through a possible playoff run. 
Because of the third-year quarterback’s adjustments and ability to beat Pittsburgh’s pressure packages, the Steelers started to lay off in the second half to their detriment, as NFL Next Gen Stats noted: 
Next Gen Stats@NextGenStatsJosh Allen came out strong in the 2nd half after struggling in the 1st half, facing less pressure and finding more open receivers.
1st Half
34.8% open throw rate, 33.3% pressure rate
2nd Half
60.0% open throw rate, 20.0% pressure rate
#PITvsBUF | #BillsMafia https://t.co/z5zuq4IV5D
Stefon Diggs became a big part of Buffalo’s second-half success. The league’s current leader with 100 receptions feasted on quick patterns to expose Pittsburgh’s weaknesses, particularly in the middle of the field where the Steelers’ second line of defense is decimated by injuries. Diggs finished with 10 receptions for 130 yards and a score. 
A year ago, this approach wouldn’t have been possible.
Obviously, the Bills didn’t have Diggs in the lineup. As good as Cole Beasley and John Brown are, they’re not true No. 1 targets, like their counterpart. A complete wide receiver corps coupled with one of the league’s best play-callers in offensive coordinator Brian Daboll is a dangerous combination. 
But the right triggerman must be in place for everything to work. 
Last season, Allen finished among the bottom half of the league in every major statistical category. He ranked dead last among qualifying passers with a 58.8 completion percentage. He became any target for detractors. The Bills got by with their running game, Allen’s athleticism and a propensity to make plays outside of structure. A top-three defense helped matters, too. 
Allen is different this year. Through hard work, due diligence regarding his mechanics and a system set up for him to succeed, the Bills found something special in arguably the most unrefined yet tantalizing talent in recent memory. His size, mobility and ridiculous arm strength are only good if they’re harnessed properly, which they have been. 
Adrian Kraus/Associated Press
With two touchdown passes Sunday, Allen now has a franchise-record 35 total touchdowns (passing Hall of Fame quarterback Jim Kelly) and counting. He’s consistently winning from the pocket with a completion percentage hovering near 70 percent while retaining those same qualities that made him such an intriguing developmental option. 
A player’s situation matters more than most are willing to give credit. Allen benefits greatly from working with the same head coach and offensive coordinator for the last three seasons. They’ve been patient. General manager Brandon Beane, who recently signed a contract extension, slowly built an excellent cockpit for Allen. He continues to reward the entire organization through his development. 
Allen jokes became easy targets since he missed so many of the same variety. He’ll still make a head-scratching play every now and again, but they’re fewer and further between and sandwiched between excellent performances. 
Instead, everyone saw what happened against the Steelers. The Bills didn’t play particularly well in the first half. Buffalo’s first-half touchdown came courtesy of a Taron Johnson pick-six. After adjustments, Allen and Co. took command of the game and finished with authority. The growth seen from the entire roster shows the squad trending toward long-term success, not just this season. But the Bills had to start by overcoming situations where they would have fallen short in recent years. 
As the 24-year-old quarterback builds his resume, the Bills could easily finish 13-3 overall after upcoming contests against the Denver Broncos, Patriots and Miami Dolphins. 
The rest of the AFC playoff picture is a quagmire. Pittsburgh fell back to the pack. The Browns must prove themselves in the national spotlight Monday against the Baltimore Ravens. The Titans and Indianapolis Colts appear to be stuck in an eternal tie for the AFC South crown. The Dolphins, Raiders and Ravens are just trying to sneak into the playoffs. 
The Bills did exactly what was expected of them this offseason. High expectations didn’t cause this team or its quarterback to falter under the pressure. Buffalo showed it’s who many thought the Bills would be thanks to Allen finally realizing his full potential.
Brent Sobleski covers the NFL for Bleacher Report. Follow him on Twitter, @brentsobleski.