BOSTON — Jayson Tatum had yet to put his mark on the Eastern Conference finals, but Brad Stevens knew it would come when the Boston Celtics needed it most — Wednesday in Game 5.

The Celtics and Cleveland Cavaliers entered TD Garden with the series knotted at two games apiece, but the 20-year-old rookie was aggressive from the opening tip, tallying 24 points on 7 of 15 shooting in the C’s 96-83 win.

Tatum hadn’t scored more than 18 points in any of the first four games of the series, but he did everything he wanted against the Cavs in Game 5. He started by getting his midrange game working before extending his assault to the 3-point line. The Duke product was locked in on the defensive side of the ball as well, using his length to get into passing lanes and disrupt Cleveland’s offense.

It’s not often that a team on the brink of the NBA Finals is relying on a 20-year-old rookie to make plays in a crucial Game 5, but Stevens knows why he’s successful on the big stage.

“I think that we misuse the word development sometimes,” Stevens said of Tatum. “I think we’re in the business of enhancement. I think Jayson was ready to deal with everything that comes with this because of who he is and his family and all his coaches before, because he’s a very emotionally steady, smart player that was going to perform at a high level at his age. I don’t know that anybody could guess this as a rookie, but you knew he was going to be really good.”

With Kyrie Irving and Gordon Hayward out for the C’s entire playoff run, Tatum has been looked to for instant offense. He is Boston’s best isolation shot creator and has shown a bevy of offensive moves from the paint to the 3-point line.

Before Game 5, LeBron James gushed about Tatum’s abilities and the Celtics rookie lived up to the praise.

Just as Stevens expected.

Thumbnail photo via Greg M. Cooper/USA TODAY Sports Images