RJ Barrett came up big in Knicks’ season-saving victory over Heat

The playoffs are revealing, the prospect of elimination even more so.

What they’ve shown about RJ Barrett is nothing but positive.

The Knicks came into Wednesday’s second-round Game 5 playing for their postseason lives, and Barrett helped keep them breathing for another day.

He’s been their most consistent player in this series not named Jalen Brunson, and helped guide them to a 112-103 must-have victory before a sellout crowd of 19,812 at the Garden.

Barrett finished with 26 points on 8 of 17 shooting, finding the rare weak spots in Miami’s defense.

He grabbed seven rebounds, played solid defense all evening in helping Quentin Grimes cool off white-hot Heat star Jimmy Butler, and helped send the Eastern Conference semifinals back to South Florida for Friday’s Game 6.

The former No. 3-overall pick has been up and down, flashing the potential that had the Knicks dreaming of All-Star berths and then hitting extended ruts.

But this postseason he’s acquitted himself well on both ends, coming against a proven veteran team and Miami coach Erik Spoelstra.

Barrett came into Wednesday averaging 19.4 points and 4.4 boards, and had upped that to 22.0 and 4.8 against the Heat while most of his Knicks teammates had struggled.

He was even better in Game 5 on Wednesday, getting to the tin, beating the 2-3 zone when Miami pulled it out and feasting in the midrange.

And Barrett’s defense was key. Grimes had the task of guarding Butler — whose 33.5 points in these playoffs were second-highest to Devin Booker — but Barrett did his fair share on both ends.

Follow The Post’s coverage of the Knicks vs. Heat NBA playoff series

Barrett’s 3-pointer capped an 18-2 blitz to start the second quarter and get the Knicks back in the game. And his two-way play sparked another game-changing 22-7 run in the third.

The Knicks were clinging to a 50-47 edge at the half that was tenuous at best. But Barrett blocked a drive by Butler, the Miami star losing a shoe and never crossing midcourt. It ended up looking like a five-on-four hockey-style power play, with Brunson drilling a 3-pointer for a 67-54 lead.

Then after another solid defensive play by Barrett and a Butler miss, the Knicks wing came downcourt and hit a dagger jumper.

Barrett ran a solid two-man game with the previously struggling power forward Julius Randle, who finally broke out with a solid game.

Barrett got position on Miami point guard Kyle Lowry, on whom he has 6 inches and nearly 30 pounds. He overpowered Lowry, and when a switch came he hit a 14-foot baseline turnaround over the outreached arms of Kevin Love.

It capped a 22-7 run, and gave the Knicks a 72-54 lead with 6:12 left in the third quarter.

His free throw on the next trip down 17 seconds later padded the cushion to a game-high 19, and they never let it go — even though it seemed they were trying to down the stretch in the fourth quarter.