BOSTON — As has become custom in these playoffs, LeBron James declared the opener of his playoff series as a “feel-out game.” James had only 15 points on 5-for-16 shooting in Game 1 against the Celtics and mixed in seven turnovers in what was one of the worst postseason games of his career.

Credit to the Celtics, who employed a switch-everything scheme that also included off-the-ball post-switches to gum up Cleveland’s offense. It was a creative scheme executed well, and now the world waits for James’ counter in Game 2.

“Usually when LeBron has these kind of games he does something legendary,” Tristan Thompson said before an off-day practice. “At the same time we can’t rely on that.”

No they can’t, but the reality is the Cavs don’t have much of a chance if James isn’t a lot more legendary in Game 2. Throughout his career, he’s made a habit of turning series around once he has a game to suss out the opponent’s strategy.

Since the Decision brought his talents to Miami, his teams have won eight of the 11 series in which they lost the opening game, with all those losses coming in the Finals. Another way to put it: He’s been down a game five times to start a series in the Eastern Conference playoffs during that stretch ... and won every time.

The legend of Game 2 LeBron has grown exponentially this postseason. Following a Game 1 loss to the Pacers, in which James shot 7-for-17, he erupted for 46 points in a must-have Game 2 that quickly passed into the James pantheon of clutch performances. Please note that James’ off night in the opener also included a 24-10-12 triple double.

The same pattern followed in the second round. James shot 12-for-30 in Game 1 against Toronto and then went off for 43 in a brilliant Game 2 performance. Again, note he had a triple-double in Game 1 as well as a game-winner. The man lives in a different universe than every other player, which the Celtics obviously understand.

“I think we’re very alert to the fact that we’ll get a heavyweight punch on Tuesday night,” Brad Stevens said following Game 1.

That will be true in more ways than one. The Cavs all but stated outright that Thompson would start Game 2 as coach Ty Lue noted his big man’s record against Al Horford.

“Over the last three years, if you study possessions, out of all the guys that guarded Al Horford, Tristan was number one in the league in defending Al Horford,” Lue said, before adding: “You guys have a great day.”

As to why Lue didn’t roll with Thompson in Game 1 — he was loathe to break up what had been an effective starting lineup with Kevin Love at the five.

“We won seven out of eight and I wasn’t going to adjust until someone beat us,” Lue said. “We had played well with that lineup and it got us to this point.”

The Celtics could counter with big man Aron Baynes in place of Marcus Morris in the starting lineup, but maybe not. Thompson had eight points and nine rebounds In 17 minutes when he and Baynes shared the court in Game 1, although the Cavs were a minus-16 in those minutes.

Starting Baynes would trigger a domino effect that would have Jaylen Brown defending James to start the game. While Brown has done reasonably well against James in the past, the Celtics like the matchup with him on Kyle Korver. They’d also prefer to have Horford stick with Kevin Love, so Stevens will have a decision to make. Starting Thompson forces their hand, but that’s what Game 2 adjustments are all about.

Of course, many of the Cavs’ problems in Game 1 were self-inflicted. Time and time again, the Cavs were slow to get into their offense, which played right into Boston’s hands. They’ll need to play with better pace in the half-court to get the C’s defense scrambling, which could open up avenues for Thompson to attack the boards on switches.

“I have to be active on the glass and tell our guys to be confident, go downhill, and attack the rim,” Thompson said. “If they miss, I’m going to try and get that offensive rebound.”

The larger concern, of course, is what James will bring to the table on Tuesday. Every defense leaves holes and it’s his job to find those openings and exploit them.

“I have zero level of concern at this stage,” he said after Game 1. “I didn’t go to college, so it’s not March Madness. You know, you get better throughout the series. You see ways you can get better throughout the series. But I’ve been down 0-1, I’ve been down 0-2. I’ve been down before in the postseason. But for me, there’s never no level of concern no matter how bad I played tonight with seven turnovers, how inefficient I was shooting the ball. I’m just as confident going into a series whether it’s a 0-0 series or I’m down 0-1.”

That’s legend talk. We’ll see if Jamescan add to his in Game 2.