Reasonable minds can quibble about when, exactly, Jayson Tatum became the best player on the Boston Celtics. There’s no official date everyone will agree on, but let’s call Jan. 11, 2020, a safe compromise. That night the Celtics beat the New Orleans Pelicans by 35 points. Tatum, who on Monday was named the Eastern Conference’s Player of the Week, scored a career-best 41 on only 22 shots. He grabbed six rebounds, tallied four assists, stole the ball three times, and did not turn it over once.

The night wasn’t a coronation, per se — it came against a putrid defense that toggled between Jaxson Hayes and Jahlil Okafor at the five, while Jrue Holiday sat on the bench in street clothes — but everything that’s happened since has been. In his last dozen games, Tatum is averaging 26.6 points, 6.7 rebounds, and 3.3 assists per game. True to form, he’s leading the NBA in plus/minus, sandwiched between LeBron James and Nikola Jokic with a 29.3 usage rate and the fifth-highest True Shooting percentage among all players who averaged at least 18 shots over that span.

Some will call this small-sample size theatre. But it feels more like a snake shedding its skin. Earlier this season Tatum really struggled to finish around the basket. That is no longer a cause for concern. Before his explosion against the Pelicans, Tatum shot just 51.6 percent within five feet of the rim, and only half of those baskets were unassisted.

Since, he’s up to 60 percent, with 62.5 percent of them created on his own. This is two things: 1) what the Celtics expected, and 2) a massive relief. Take that one drawback away and what you have is a near invincible 21-year-old who was recently named to his first all-star game. Tatum leads Boston in several categories, including minutes, shots, points, defensive rebounds, and usage.

Comb through NBA history and you won’t find too many third-year players who led their team to a championship, let alone the Finals. But Tatum is positioned to try. His two-way contributions impact nearly every area of the modern game that relates to wins and losses; he’s built to thrive in a playoff atmosphere, with an untouchable combination of size, feel, strength, aggression, and pinpoint footwork that would make a Broadway choreographer blush. All that is terrific, and makes slowing him down on a team that also has Kemba Walker, Gordon Hayward, and Jaylen Brown unimaginably difficult.

But Tatum’s most significant stride comes in the form of his pull-up three, a skewering harpoon every elite scorer should be able to pull out of their bag whenever they want. Among all players who launch at least four pull-up threes per game, only Damian Lillard is more accurate than Tatum’s 39.2 percent this season. It’s a game-changing stresser that, by itself, raises Boston’s collective ceiling.

These shots account for a whopping 22.7 percent of Tatum’s repertoire, up from 10.7 percent last year and 7.8 percent when he was a rookie. (Right now he’s taking more pull-up threes than pull-up twos — that’s not nothing.) He’s improved on the defensive end and as a playmaker, but this shot is Tatum’s golden ticket to megastardom. He hasn’t mastered it fully, but is well on his way.

Now, zoom out to compare Tatum with the select few who led their team deep into the playoffs during their third year and what makes him so remarkable is how pretty much none of Boston’s roster was built with him specifically in mind. He’s an integral puzzle piece, but so are Brown, Hayward, and Walker. They all help each other in Brad Stevens’ whirring drive-and-kick offense, a system that doesn’t go out of its way to lean on Tatum’s virtuous skill set but should tilt more and more in his direction during the playoffs. In more ways than the general consensus probably expected, he’s helped fill the void that was left by Kyrie Irving and Al Horford.

Among all players (54, to be exact) who finish at least five possessions every game as a pick-and-roll ball-handler, Tatum is the ninth-most efficient scorer and ranks in the 86th percentile overall. He glides downhill at his own pace, crouching down to put his defender in jail, waiting to punch through a crack. Tatum averages more points per possession in these spots than James Harden, LeBron James, Devin Booker, and Paul George. (Everyone above him is a true point guard, except Luka Doncic and DeMar DeRozan.)

On a team that believes it can win the whole thing — Boston is currently third in point differential and defense, fifth in offense — every bit of improvement from Tatum is a step closer to reaching their goal. But in this particular context, what does his growth actually mean?

If you hesitate to call the Celtics a true contender it’s probably thanks to precedent. They entered the season with the deepest wing rotation in a league that prioritizes that position. Walker, Brown, Tatum, and Hayward all either had a chance to make the all-star team or an appearance already on their resume. But none were a top-15 player, let alone a top-seven or eight superstar that’s typically needed to win it all.

Tatum can change that. For the season, he stands firm in Real Plus-Minus’ top five, bested only by arguably the four best players in the NBA. Beyond statistics, he’s often guarded by the opposing team’s best defender, a magnet of attention who allows his all-star-caliber teammates to feast on thinner coverage than they otherwise would. When he sets a ball screen — particularly for Walker — defenders can’t trap it then rotate a third man over because giving Tatum a step against a closeout is certain death, as is the fraction of a second in which he finds himself wide open behind the three-point line. In these subtle ways he’s a complementary piece as much as he is a leading man.

With off-ball gravity that’s steadily rising towards the same level seen by some of the league’s top scorers, when Tatum moves his teammates reap a clear benefit.

His improved defense cannot be taken for granted, either. Tatum doesn’t just hold his own on that end, he alters what the offense wants to do. Stevens will often stick him on a squirrelly point guard so that when a big sets a screen the Celtics can either switch it without creating an obvious mismatch, or have him fight over/under the screen and still affect the shot. You could kick a field goal through his outstretched arms.

There are still baby deer moments scattered through his touches, but they announce themselves as necessary mistakes instead of permanent flaws. Tatum’s encroachment towards actual greatness isn’t hard to see, even when he turns the ball over in a crowd or fumbles a sure layup off the wrong angle. In the clutch he’s in the 50/40/90 club, with a usage rate that’s six percent higher than last year.

Night after night, Tatum continues to excel in areas that can’t be taught. He’s finishing with both hands, reading defenses with a patient maturity that’s had by every great player who understands what his team needs at any given time.

Whether that be blowing the roof off TD Garden with a side-step three, freezing a defender with a humbling hang dribble that gets him to the free-throw line, or chasing the opposing point guard through screens and unlocking aspects of a switch-happy, swarm-and-rotate defense that will translate against any offense in the postseason.

Among third-year stars, he’s probably not on the same level as 2006 Dwyane Wade or 1994 Shaquille O’Neal, but has a larger role than Manu Ginobili did in 2005 or James Worthy in 1985. Time will tell if he actually uses these playoffs to make the substantial leap his recent play indicates he’s ready for, to do something Russell Westbrook and Derrick Rose couldn’t in 2011, when their teams bowed out in the conference finals.

Until then, Tatum is the portal Boston’s otherwise excellent ensemble needs to someday win it all. His steady encroachment towards his own MVP-level end game begs the question: Why can’t he be the third best player in his conference — behind Giannis Antetokounmpo and Joel Embiid — three months from today?

Take everything he’s doing — and everything we already saw during his first taste of the playoffs, when he set all sorts of records on a memorable playoff run to the Eastern Conference Finals that was littered with epoch-worthy exclamation points — and it’s not hard to picture Tatum exiting the postseason as that alpha catalyst all title winners need, on a team that can be one. Give him the ball and get out of the way. Good things are happening when the Celtics do.