So you want to prove you are championship caliber? Celtics, here is your chance.

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So you want to be a champion. Here is your chance to prove it.

There are so many ways to spin what Game 5 of this best-of-seven series against the Raptors means to the Celtics. Sure, it can be perceived as important because of the obvious upper-hand delivered to the victor Monday night.

But it's more than that.

There are few singular moments you can firmly identify the maturity and mindset of a group. This is one of them.

What we know is this ...

1. The Celtics looked like the far superior team all the way up until Kyle Lowry lofted that pass over Tacko Fall's fingertips.

2. Since then Toronto has offered the reminder why even without Kawhi Leonard they are still living life as world champs.

3. Nick Nurse has gotten the better of Brad Stevens since that Game 3 dagger, taking the Celtics' offense completely out of rhythm with a variety of zones and good ol' fashioned defensive grit and guile by his players.

4. This is going to be stars vs. stars, with three players from each side playing more than 40 minutes in Game 4 (with Jaylen Brown clocking in at 37 minutes). If the Celtics' core players step up like they didn't do Saturday night, Stevens is going to enjoy the results.

5. The Raptors feel really, really good about themselves.

OK. Those are the facts.

What we don't have good grasp on is exactly what this Celtics team is all about. We thought we did, but until this group stares down all of the aforementioned realities and manages to rekindle last week's optimism all that remains is doubt. The same kind of doubt that the C's wore in previous seasons, heading into this campaign, at the outset of the bubble and throughout the first few games of this postseason.

They are such a more functional group without Kyrie Irving. Jayson Tatum and Jaylen Brown are ready to take the next steps. Kemba Walker is the perfect complement. Brad Stevens finally has his perfect combination of talent and chemistry. They ARE ready for that championship conversation!

All of those were narratives that had become easier and easier to circulate with each passing day. But maybe this is the unexpected lesson that still had to be learned. Maybe this team - its players and its coach -- isn't ready to enter into such a stratosphere.

It is just one game and if the Celtics lose there will still be another. But these are the sort of moments that allow for true character to be revealed. Just ask Toronto. The Raptors had to plow through such obstacles on their way to that championship.

Nurse's team lost their first playoff game last year. They were forced to claim a Game 7 against the Sixers in the second round. And the Eastern Conference finals had to be claimed after dropping the first two games vs. Milwaukee.

The Celtics? Last season they won their first five playoff games before dropping four in a row on the way to an uninspired exit. This year all was right with the world via six straight wins before OG Anunoby's shot. Since then, it's been uncomfortable.

Stevens' team has shown resilience in past postseasons, having rebounded from two straight losses after winning the first two against Milwaukee in the first round two seasons ago. But that Bucks weren't the defending champs. Far from it. And that Game 7 win over the Wizards the year before that? Nice but ...nope. The series' might look the same this time around, but's not.

Of all the opportunities the Celtics have had to truly define what they are and where they are going, Monday night's Game 5 separates itself. No more talk. No more predictions. No more guessing.

It is what it is, and what it is is a defining moment for this collection of Boston Celtics.

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