The mantra has already started: “It’s only one game.”

That’s a perfectly understandable reaction by Bills fans following Tuesday night’s embarrassing 42-16 loss to the Titans in Nashville.

But while they’re factually right, there’s also a bit of whistling past the graveyard at work.

Falling to an unbeaten team — Tennessee was 3-0 coming in — is hardly reason for panic.

But, given the circumstances, concern is certainly in order.

Buffalo was manhandled by a short-handed Titans team that was without seven players from the active roster due to Covid-19, including the Nos. 1 and 2 wide receivers, with the No. 3 wideout playing through a knee injury.

Despite that, coach Mike Vrabel opted to attack the Bills through the air — Buffalo was in the bottom third of the league defending the pass — knowing their two starting cornerbacks (Tre’Davious White and Levi Wallace) were out, as was their top coverage linebacker (Matt Milano).

Thus, Titans quarterback Ryan Tannehill defrocked Wallace’s replacement, Josh Norman, who played horribly. He threw to injured veteran A.J. Brown and a bunch of receivers you never heard of, to hand the Bills their most one-sided defeat since a 41-9 clobbering by Chicago in November of 2018 and its worst road drubbing since two games before that, at Indianapolis (37-5).

But what made it more galling was that Tennessee was seemingly in total disarray for being the NFL poster child for mishandling the coronavirus (24 organizational positive tests, 13 of them players). The Titans had conducted only one practice, other than the alleged unauthorized workouts, in the previous 16 days.

Worst of all, the Bills, who were admittedly in practice limbo not knowing whether their next opponent would be the Titans or Chiefs, didn’t appear to be ready to play Tuesday night.

They were flagged 14 times — one was offsetting, another was declined — and, of the other 12, seven were concentration failures, four false starts and three encroachments.

A pass interference against Norman kept a touchdown drive alive and a roughing-the-passer call on defensive tackle Quinton Jefferson did the same.

On offense, an illegal shift cost Buffalo a touchdown pass to rookie Gabriel Davis, though the Bills still eventually scored on that drive.

But those are only some of the gaffes that had coach Sean McDermott seething and made for a tough Wednesday film review.

FOR McDERMOTT, a coach with a defensive pedigree, his ‘D’ has to be a continuing source of annoyance and frustration.

Clearly, losing White (back), Wallace (ankle), Milano (hamstring/pectoral) and middle linebacker Tremaine Edmunds (shoulder) for various amounts of time has been punitive.

But, even at that, Buffalo’s defense hasn’t been anywhere near the unit it was the past two years.

That struggle was somewhat overlooked as quarterback Josh Allen’s incredible performance in leading the Bills to a 4-0 start somewhat masked their defensive shortcomings. But with Allen enduring a pedestrian effort against the Titans, Buffalo’s flaws on defense were as obvious as a motor scooter at a Harley-Davidson rally.

For the record, through five games, the Bills are surrendering just over 28 points per game (tied for 21st in the league) and giving up 263 yards through the air (24th).

But, over the past four games the numbers are much worse.

In that span, Buffalo is giving up 31 points and 401 yards per game and the loss to Tennessee is a reminder that Allen can’t be expected to carry this team every week … he’s entitled to a tough game.

And, it’s not just against the pass. The rushing ‘D,’ since the opener against the Jets, is giving up 123 yards a game, a figure that, at best, would put it in the middle of the NFL. This from a team that was No. 2 in the league for total defense a year ago.

THE REALITY is this.

After losing so decisively to the Titans, a reexamination of Buffalo’s schedule is in order.

On Monday, the Bills host the defending Super Bowl champion Chiefs, who are a 3.5-point favorite. And still to come are cross-country trips to Arizona (Nov. 15), San Francisco (Dec. 7) and Denver (Dec. 20) plus home-and-home meetings with the Patriots and a pair of unbeatens visiting Orchard Park (Seattle, 5-0; Pittsburgh, 4-0).

And what happened Tuesday night in Nashville is a stark reminder that there are no guaranteed wins.

(Chuck Pollock, a Times Herald senior sports columnist, can be reached at cpollock@oleantimesherald.com)