A reminder on The Horry Scale: It breaks down a game-winning buzzer-beater (GWBB) in the categories of difficulty, game situation (was the team tied or behind at the time?), importance (playoff game or garden-variety night in November?) and celebration. Then we give it an overall grade on a scale of 1-5 Robert Horrys, named for the patron saint of last-second answered prayers.

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The Knicks and Celtics have been mired in mediocrity this season, battling upward against expectations, injuries and this never-ending pandemic. Each team entered the game at 18-20, with 10th place — the final Eastern Conference Play-In Tournament slot — in the balance.

Celtics foil Evan Fournier did even more than his usual damage, scoring a career best 41 points after putting up 32 in each of the prior games vs. Boston. His electrifying outburst, along with a second-half surge by Julius Randle (15 of 22 points after the break) helped the Knicks close a 25-point gap and set the stage for Barrett’s unexpected heroics.

The third-year swingman was grinding his way through a 3-for-14 shooting performance, finding subtle ways to contribute in the clutch, notably helping to burn nearly 20 seconds of clock before suckering the Celtics into a shooting foul with 18.8 remaining and the Knicks holding onto a slim lead. A heady play! (He promptly missed the first free throw. That kind of night.)

Until it wasn’t.

GAME SITUATION: The Knicks looked cooked through halftime, and even into the third. But a 16-3 run to close the quarter whittled a 25-point deficit to seven, and the momentum continued to tumble from there, to the growing delight of The Garden crowd.

By the time Evan Fournier gave the Knicks their first lead of the game at 99-98 on a completely ridiculous catch-and-shoot corner 3 as he faded across the sideline, Knicks Twitter was losing its collective mind. And though the Knicks could’ve put things away at the line — both Barrett and Randle split a pair of free throws in the final minute — they were up enough to be tied with time to win it.

With red-hot Fournier the obvious cover, RJ entered the chat.

Game winner at The Garden.

Nothing like it. pic.twitter.com/H4Wwr2KQAA

— NEW YORK KNICKS (@nyknicks) January 7, 2022

DIFFICULTY: The 1.5 seconds left by the fates — and Jayson Tatum’s game-tying pullup — would’ve felt more restrictive had the Knicks not saved their final timeout on the possession prior. Advancing the ball into the frontcourt, as Alec Burks looked to inbound, Immanuel Quickley broke toward the baseline from the top of the key. That drew Jaylen Brown away from Barrett, who cut parabolically from left wing to right, making the catch as Jayson Tatum closed in perfect position to contest. With no option but to let fly, Barrett used his 1-2 to keep his momentum toward the sideline, falling away out of bounds as it banked home.

CELEBRATION: Barrett rolled into the padding just beyond the Knicks bench, so he popped up into an onrush of a whole team’s worth of jubilation. As they bounced joyously, Celebrity Row lit up, with Fat Joe exulting and Tracy Morgan just looking for someone to hug.

GRADE: They’re in 10th! They’re in 10th! It’s but a step in the playoff-return process, one can suppose. But a fun way to get there nonetheless. Four Horrys.