CLEVELAND >> J.R. Smith reached out, placed his hands on Al Horford’s back and shoved Boston’s big man out of bounds.

It was the only time Smith was on target.

Smith’s shoddy performance in Game 2 — he missed all seven shots and committed a flagrant foul in 27 forgettable minutes — underscored a startling disparity between Cleveland’s and Boston’s starting backcourts that allowed the fearless Celtics to withstand a brilliant, 42-point effort by LeBron James and take a 2-0 series lead.

Smith and point guard George Hill were outscored 41-3 by Boston’s Jaylen Brown and Terry Rozier, who were faster, hungrier and maybe tougher.

“I don’t think tougher,” Smith said afterward, showing better defensive instincts than during the game. “They made shots, we missed shots at the end of the day. We had some good looks, they didn’t fall. For them playing on their home court, they fell. It’s a matter for us to bounce back, go home, try and get (win) two, even the series up and come back here.”

Thanks to the NBA’s odd scheduling, Game 3 is not until Saturday, giving Cavs coach Tyronn Lue plenty of time to consider tweaks to his starting lineup and rotations. After a 25-point lambasting in the opener, Lue altered his frontcourt by putting Tristan Thompson with the first five and bringing Kyle Korver off the bench.

The moves worked as Thompson provided needed energy and Korver knocked down four 3-pointers and had Boston’s defense focused on more than James.

Now, Lue has to ponder another shake-up.

One option is to re-insert Korver at small forward, sit Hill and slide James to the point, where he typically plays anyway but where he’ll be more susceptible to double teams and will have to work harder than he is already.

Another possibility is to drop Smith, who is 2 of 16 from the field and missed all seven 3-pointers, from the starting lineup, but that would be risky because of his mercurial nature. Sit him and risk never getting him back.

Lue is willing to live with Smith’s streakiness — he went 6 for 6 in Game 4 against the Raptors — but what he can’t afford are the defensive lapses that led to slow rotations and gave Rozier and others wide-open looks in Game 2. Smith has been locked in defensively throughout the postseason, so Lue is assuming he’ll get it together.

Lue’s decision not to play guard Jordan Clarkson for a single minute in Game 2 was curious, mostly because Clarkson is quick enough to handle Rozier and he scored 10 points in Game 1.

Veteran Jose Calderon appears to be out of consideration despite his steadiness and experience. Lue may fear the 36-year-old will be targeted and exposed defensively.

Of course, there’s irony in Cleveland having backcourt issues in this series.

A year ago, Kyrie Irving averaged 25.8 points in the Cavs’ five-game rampage over the Celtics in the conference finals. Now an injured Irving sits on Boston’s bench in street clothes unable to help his new teammates while his presence teases the Cavaliers, who have not adequately replaced the All-Star since trading him.

They are finding life in the playoffs is more difficult without Irving, who at times carried Cleveland’s offense, giving James a break and Lue a dependable second scoring option.

It’s easy to second-guess the decisions now, but it feels as if the Cavs’ trades of Derrick Rose and Dwyane Wade at the deadline were hasty. Cleveland lacks enough playmakers capable of creating their own shot or opportunities for others.

Hill has been unusually passive in the first two games, and the Cavs need to get him going.

And they certainly need more from Smith, whose frustration surfaced at the worst possible time when his hard foul on Horford riled up the Celtics and their rowdy crowd.

As the referees reviewed the play, Boston fans chanted profanely at Smith, who smirked and later said the taunts didn’t bother him.

“I love it,” he said. “I don’t want the opposing fans to like me. That’s not why I’m here. They can chant and scream all they want. It actually makes me feel better about myself. They know me.”

The Cavs know him better, and they need Smith to be himself.