Sunday’s Patriots game at Buffalo will serve as the ultimate litmus test for the Bills — who are basking in their first 3-0 start since 2011, matching New England’s 3-0 start.

The winner of this matchup takes early control of the AFC East.

The Bills, who are 3-0 for the ninth time in team history, are not being taken seriously as contenders because the record of their three opponents — the Jets, Giants and Bengals — is a combined 1-8.

Interestingly, though, the Patriots have not been subjected to the same scrutiny despite the fact their three wins have come against the Steelers, Dolphins and Jets — a combined 0-9.

Unlike the Bills’ fast start, the Patriots have dominated their three opponents, with a defense that has not allowed an offensive touchdown. Last Sunday, they held the Jets to 105 yards on offense — the fewest total allowed by the Patriots in the 347 games Bill Belichick has coached themincluding postseason.

“No one’s come close to even touching them at this point,” Bills coach Sean McDermott told reporters this week.

The New England defense is the first in the Super Bowl era to not allow an offensive touchdown in the first three games of a season. Granted, they played Jets third-string quarterback Luke Falk Sunday, the Dolphins’ Ryan Fitzpatrick and Josh Rosen duo and Pittsburgh’s Ben Roethlisberger.

The Patriots, ranked No. 1 in the NFL in fewest rushing yards, passing yards and total yards allowed, have allowed a 13.6 percent conversion rate on third downs, and 33 of 37 drives against them have ended in punts or turnovers. These numbers are thanks to an NFL-high 13 sacks, 10 quarterback hits and 27 hurries, according to Pro Football Focus.

“We understand it’s a tall task, but at the same time we’re going to try and stick to what we do,’’ Bills quarterback Josh Allen told reporters after Buffalo’s 21-17 win over the Bengals.

“It’ll be a challenging week ahead,” Bills offensive coordinator Brian Daboll, a former assistant of Belichick’s New England staff, told reporters. “It’s kind of unprecedented, what they’re doing on defense right now.”

The task of the Bills’ defense doesn’t figure to be much easier. They’ve lost 30 of the 33 games they have played against Tom Brady, whose thrown 69 touchdowns to just 24 interceptions against them. Brady’s 30 wins over the Bills are the most by an NFL quarterback against one team in league history. He has 28 wins against the Jets.

The Bills are ranked No. 1 in the league in fewest yards allowed per drive (24.8), third in touchdown percentage per drive (16.8) and No. 1 in percentage of three-and-outs forced (36.2).

Offensively, the Bills have been inconsistent. Allen has completed 66 of 103 passes for 550 yards with three TDs and three interceptions.

Frank Gore has looked ageless with his 44 carries for 164 yards and two TDs.

Last season, the Patriots won 25-6 in Buffalo and 24-12 in Foxborough.

According to ESPN, this is the first time an undefeated Bills team will play against a team with a record of 3-0 or better since 1992, when they lost to the Dolphins.

They’ll hope the result is different this time. And if it is, the Bills will have validated themselves as a legitimate contender in the AFC.