The Celtics’ Paul Pierce watches from the bench after fouling out late in Game Six on Friday night. Game Seven starts at 1 p.m. today and will be televised on ABC 6.

The Providence Journal / Glenn Osmundson

It wasn’t supposed to be this way, of course.

The Celtics weren’t supposed to be in a Game Seven with the Atlanta Hawks, a young team that won only 37 games this year, and were supposed to already have been as gone as the Easter bunny.

The Celtics weren’t supposed to be life-and-death with a team that was lucky to be in the playoffs, never mind be in Game Seven with a team that won 66 games, the best in the NBA; a team that will come into the Garden today with absolutely nothing to lose.

Which is the bottom line here.

Yes, the Celtics should win today. Yes, the Hawks have already lost three games in the Garden by an average of 22 points, have shown no indication that they can win a playoff game on the road, never mind one in the hothouse that’s become the Garden in these playoffs. Yes, a week from now this may seem like much ado about nothing, a minor inconvenience.

But all the pressure is on Boston this afternoon, not just for this series, but for this franchise, too.

For this season has been a wonderful rebirth of the Celtics. This was the year they burst back across the radar screen, became relevant again, no longer buried beneath the Red Sox and the Patriots. This is the year they are supposed to bring back the glory days.

That’s been the promise, ever since last summer when the Celtics brought in Kevin Garnett and Ray Allen and the world changed. They were going to join with Paul Pierce and become the new Big Three. They were going to bring back the Celtics as they once were, back when big games in June were part of the schedule and it was all about championship banners hanging from the rafters, nothing else.

That’s what this is supposed to be about, fair or not.

Not the fact that the Celtics won 66 games this year.

Not the fact they had the best regular-season record season.

Not the fact that Kevin Garnett was the defensive player of the year.

Not the fact they sell out the Garden again, every game a love fest.

Another world title.

That’s the standard here, the reality of being the Celtics, where for too long now those 16 championship banners have hung down like accusers, a constant reminder that once upon a time the Celtics were the best of the best.

For we measure success here in titles, fair or not. This is not Orlando, not Sacramento or Atlanta, not even Dallas, places where there is little history, and to go to the playoffs is a big deal. This is Boston, where the history is right there in the rafters. All you have to do is look.

Boston, where the expectations are huge, and where the theme of this season has been the drive for number 17.

Boston, where a loss to the Atlanta Hawks this afternoon will be viewed as one of the worst playoff losses ever, the kind of ignominious defeat that will all but render all those 66 wins meaningless.

That’s what’s on the line today, and not just for the perception of this franchise. Number-one seeds are not supposed to lose to number-eight seeds, and there’s no doubt that if the Celtics lose this afternoon there will be a big target on Doc Rivers’ back. That comes with the territory.

And not just Rivers.

The players, too.

Especially the Big Three.

They are the face of the franchise, the three guys that are billed as this generation’s version of Bird, McHale and Parish. They are the core of this team, the three that are supposed to lead this team into big games in June. And if this team puts the balls away for the summer this afternoon they will take heat, too.

As well they should.

For they are not Bird, McHale and Parish, not yet anyway. They are not for the simple reason that they not won anything yet, not anything significant. Wasn’t that the theme of their first press conference together last summer? Wasn’t it about the fact that for all their success and basketball fame, none of them had won a championship? Wasn’t that their goal, the reason they were going to be able to subordinate their egos for the chance to win together?

That, too, has been the promise. But Friday night Pierce fouled out on a stupid foul on a rebound with 4:44 left, then trumped it by getting a technical foul, courtesy of a thrown headband. This is the captain? Then Allen took an ill-advised three with 12 seconds to play.

Then there’s Garnett.

Yes, he’s a great player, as versatile a big man as you’ll see anywhere, but he’s not a dominant inside scorer, someone who gets the ball in crunch time and flat out puts it in the basket. And if he doesn’t do that, then what? The Celtics then become a jump-shot team, live by it, die by it, too.

For one thing’s been revealed, regardless of how this afternoon plays out: the Celtics are vulnerable in ways the regular season masked. They are not as athletic as the Hawks, which has come as a certain surprise. They are not as deep as we thought, not as good as their 66 wins would suggest.

Still, this is Game Seven in The Garden, a place where the Hawks have not been competitive in three games. This is a game the Celtics should win, even if they weren’t supposed to be in this situation.

Game Seven at home, a game the Celtics had better win, or else the 66 regular-season wins get wiped off the board, as irrelevant as a pregame layup drill, dust in the wind.

breynold@projo.com