BOSTON — Coach A has seven seasons studying as an assistant under decorated coaching legend Gregg Popovich and another season as an assistant coaching Joel Embiid and Ben Simmons on the Philadelphia 76ers.

Coach B is one of the best point guards in NBA history who spent two seasons as a player development consultant with the Golden State Warriors but has no formal experience as an assistant coach anywhere. He worked with Stephen Curry, Klay Thompson, Kevin Durant and Draymond Green, but did not lead them on a nightly basis.

The Nets hired Coach B two seasons ago and made Coach A his understudy. Now Coach A is getting his revenge.

Coach A, aka Ime Udoka, just thoroughly outsmarted, out-adjusted and out-gameplanned Coach B, aka Steve Nash, to lead his team to a 2-0 first-round series lead in the playoffs.

Nash does not have any answers for Udoka’s adjustments.

“I think in hindsight you could always come up with something,” Nash said Wednesday. “But there’s no guarantee that whatever your adjustment is is going to work, so it’s 20-20 looking backwards.”

What’s becoming increasingly clear as the Nets struggle in their first-round series against the Celtics is that the right man for their head coaching job now wears green and white, when the Nets had an opportunity to dress him in black and gray.

Ime Udoka is a Coach of the Year candidate who transformed the Celtics into the league’s best defense and righted an 18-21 start to Boston’s season with a 33-10 sprint to the finish.

Through two games, Udoka has solved the league’s most difficult puzzle. His team’s defense has turned Kevin Durant over 12 times and held him to just 13-of-41 shooting from the field.

“They’re doing a good job of trying to cut off my scoring, trying to limit my shot-making,” Durant said postgame. “Two or three people contest and there’s somebody there in the lane when I’m driving. They might double here and there, so they’re doing a good job and it’s on me to figure it out.”

The Nets need Durant or Kyrie Irving, and preferably both, to score 30 or 40 every night for this team to have a chance to win a playoff game. One game after Irving erupted for 39 points in the Nets’ one-point loss to the Celtics in Game 1, Udoka’s defense held him to just 10 points on 4-of-13 shooting from the field.

“Ime knows us really well,” Irving said postgame. “You know, he coached on our staff last year, so I think he has some keys in the treasure chest that he’s telling those guys.”

It should be on the head coach to figure out the opposition’s schemes and create a strategy against it. Nash said earlier in the season he’d be “one hell of a coach” if he could figure out how to get the most out of his players. Up the sidelines in green and white is what one hell of a coach looks like.

The Nets could have hired that standout coach. Udoka’s trajectory was predetermined by his resume. He was a sure bet as an elite NBA coach. Instead, the Nets bet on a rookie head coach, and what has ensued has been predictable.

For the second consecutive season, Nash has appeared in over his head as the head coach of a team with championship-or-bust expectations. He has ridden the coattails of his two superstars, only to fall short every time they haven’t been available or played up to par. He has struggled to adjust to adjustments and runs a junior varsity-level offense, in part because the Nets have not had time to build a more complex offense with roster turbulence this season, but also in part because he’s relied on his stars to create plays for themselves and others so frequently this season.

When Udoka neutralized those stars, Nash looked helpless, downright despondent, after the Celtics turned a 17-point Nets lead into a 12-point fourth-quarter advantage of their own to secure a Game 2 victory to take a 2-0 series lead.

“Well, clearly it helps if (Durand and Irving) have their typical outings, but that’s not the only way (we can win),” Nash said. “I think there’s plenty of ways (to win). Their superstars didn’t have incredible games, so it’s a team sport, it’s a team effort and I think our group’s got a lot of ways where we can improve.

“It’s important for our group. It’s a new team with little common experiences to go through some of these battles, learn from it and be able to execute under more pressure.”

Udoka’s predictable emergence creates another what-if in Nets history. Forget about what if the Nets never traded James Harden. What if they hired Coach A instead of Coach B?

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