Ten days ago, the sky was falling on the Giants.

They were 0-2 after having lost consecutive fourth-quarter leads, and fans and sports radio savants were ready to send a bus to their training facility to transport their 69-year-old head coach to a nursing home.

With a win over the Bills in Buffalo on Sunday and a Cowboys loss to the Saints, the Giants could wake up Monday morning tied for the best record in the NFC East.

It’s early in the season, but Sunday’s game against Rex Ryan’s 2-1 Bills at Ralph Wilson Stadium qualifies as pivotal and potentially season-shaping for the 1-2 Giants.

There’s a notion — ill-conceived as it may be — the Giants are going to get bullied by Ryan’s Bills and their formidable defensive front.

Why? When exactly did the Bills elevate to among the league’s elite?

This is a team that was getting waxed by the Patriots at home two weeks ago before a garbage-time rally in the final quarter after New England had lost interest. That rally turned the score into one that was not indicative of how much better the Patriots were.

The Bills rebounded last week to dominate the Dolphins, but let’s be honest: The Dolphins are an underachieving, dysfunctional bunch with a head coach on the hot seat.

The Bills will face the Giants without their best running back, LeSean McCoy, out with a hamstring injury, and their best receiver, Sammy Watkins, out with a calf injury. Their quarterback, Tyrod Taylor, is a work in progress with the talent to make big plays, but vulnerable to disguised looks on defense.

A win would give the Giants a 2-2 record at the quarter-pole of the season. With the 1-2 Eagles playing the 1-2 Redskins, the winner of that game will be 2-2. A Cowboys loss to the Saints would make Dallas 2-2 and still without Tony Romo for a while.

Suddenly, despite their flaws, the plight of the Giants doesn’t seem nearly as grim as it did 10 days ago — despite the nagging Victor Cruz calf injury that becomes more disconcerting by the day.

“I didn’t really make too much of the hysteria that was going around the first couple of weeks after two losses,’’ running back Andre Williams told The Post on Friday. “From the beginning, the losses hurt. But when I watched the games, we played ahead until the fourth quarter the first three games of the season. We’re going to continue to get better, continue to learn how to finish as a group.’’

Asked about the opportunity to tie for first in the division with a win this weekend after things looked so bleak such a short time ago, Williams said: “The win is going to be great, but the tie for first place won’t really satisfy me, because we’d be tied with the team [Dallas] that we had beat [in the opener] and haven’t beat yet this year.’’

Here is the Giants’ formula for success: Smack Ryan’s Bills in the mouth first, before the Bills have a chance to smack them. This is always the best way to neutralize a supposed bully. It also will slow the Bills down, because Ryan is a front-running coach whose teams reflect his personality.

The Patriots took it to the Bills early and silenced the raucous home crowd until it was too late.

“Yeah, he’s got that attitude,’’ defensive tackle Cullen Jenkins said Friday of Ryan. “He’s got that attitude, and the team does, too. We want to go out and show people that we’re just as physical as any team in the league. We’re trying to earn respect in our own right and come into our own identity.’’

Last week’s win over the Redskins was a start. A win Sunday in Buffalo would validate that first win. The last pattern the Giants want to fall into is the dreaded, one-step-forward, one-step-back mode.

“It got us on the right track with a win,’’ Jenkins said. “Now, we’ve got one and we’re trying to carry the momentum from that, trying to get another one this week.

“There’s been a lot of craziness going on in the division with a lot of injuries and different things. We’ve just got to try to take advantage of the opportunities we have. If we do that we should be able to be in the position we want to be in.’’