Earlier in his career, entrusting J.R. Smith with defensive chores on your opponents’ most potent scorer would have as sound strategically as designating Isaiah Thomas to protect your rim or putting the ball in Andre Drummond’s hands in late-game, defense-has-to-foul situations.

That was then, this is now: Smith is halfway through his second playoff series this spring as the Cleveland Cavaliers’ primary on-all defender. In the first round against Indiana, Smith was matched up with Paul George. Currently, he is Cleveland’s first line of defense on Toronto’s DeMar DeRozan, whose struggles have the Raptors down 2-0 and desperate to spring loose their leading scorer (27.3 ppg) in the regular season.

“I absolutely enjoy it,” Smith said. “Definitely I look at it as a challenge for myself and my team. I mean, we’ve got guys who can score and all that, but we really need guys who can make plays on the defensive end. I take pride in that.”

Smith said that prior to Game 2 Wednesday, he put his game where his mouth was through the evening. DeRozan had a miserable game, scoring just five points and making only two of his 11 shots. When Smith checked out for good after three quarters, the Raptors’ frustrated All-Star had missed all nine of his field-goal attempts and had just one point.

To get even more specific, according to SportVU tracking data, DeRozan is 0-for-8 with a mere three points in the 12 minutes 20 seconds Smith has been guarding him. When Smith has been out of the game, DeRozan has made 55.6 percent of his attempts. With Smith on the floor, that drops to 22.2 percent.

And in the two games of this East semifinal series, DeRozan is a minus-53 in 66 minutes. Smith? He’s a plus-43 in 54 minutes.

“He’s given an assignment,” Cavs teammate LeBron James said of Smith. “Coach [Tyronn] Lue challenged him, giving him an assignment on Paul George in the first round, on DeMar. That’s two of the best two guards we have, especially in the Eastern Conference.

“We’ve tried to just communicate on the back line of defense ... just let him know that we’re protecting him or what’s coming up or what’s going on behind him. He’s taking the challenge, so we just want to continue to do that.”

Much was made last June, in Cleveland’s Finals showdown with Golden State, of Smith’s conversion from a conscienceless gunner to a more reliable two-way player. He gave much of the credit then to a conversation with his young daughter Demi, who inadvertently turned a teaching moment about sacrifice back onto her dad.

But the payoff that came from doing that, including an NBA championship ring, locked in the incentive for Smith. So, too, did the sense of living up to standards set and demonstrated by James. In Smith’s New Orleans, Denver and New York stops, there wasn’t anything from a leadership standpoint to push him quite like that.

“When you’re playing for championships, you definitely have to pick your game up,” said Smith, 31. “When a team is as talented as this one is, you get challenged by your teammates to raise your game every day.”

The Cavaliers have deployed gang tactics on DeRozan to tighten the defensive screws even beyond Smith’s individual work. Like George in the last round, the Toronto guard has been blitzed, trapped and corralled by extra defenders, forcing him to give up the basketball or risk a turnover (he had four in Game 1).

When Smith sits down, Iman Shumpert typically takes over. The option of shifting James onto DeRozan remains, similar to what Lue did late in games against George. But Smith’s ability not to get burned keeps James away from foul trouble and, in Lue’s opinion, frees him to play more randomly on defense while stealing some rest.

If that has helped to energize James’ performances so far – he’s averaging 34.2 points, 9.0 rebounds and 7.3 assists in the playoffs while shooting 56.6 percent – then Smith’s defensive work has been a win-win for the Cavaliers.

That Smith’s own offensive production has been meager – 2-for-4, six points in both Game 1 and 2 – hasn’t even come up. As a younger player, he might have griped about touches or sulked.

“It just took me a while,” Smith said before this series began, “to kind of grasp that that could be my niche.”

Steve Aschburner has written about the NBA since 1980. You can e-mail him here, find his archive here and follow him on Twitter.

The views on this page do not necessarily reflect the views of the NBA, its clubs or Turner Broadcasting.