First the Nets lost their best scorer. Then they lost a heartbreaker to basketball’s best team.

Hours after finding out Cam Thomas will miss the rest of the season, Brooklyn was edged 115-113 by reigning champion Boston in front of a sellout crowd of 18,016 at Barclays Center.

“We all want to win. And the reality is when you lose, you’re not happy,” said Nets coach Jordi Fernández. “There’s no moral victories here, but if that’s going to be our identity, a lot of good things are going to happen.”

The Nets (22-45) have dropped 10 of their past 11 games. Their prior four had been by a combined 16 points; this was even closer.

Cam Johnson — who had 23 points, 10 rebounds and six assists — hit a 3-pointer to pull Brooklyn within one with :04.5 left. Payton Pritchard (22 points) hit one of two at the line, and Johnson couldn’t beat the clock with a last-ditch heave.

Brooklyn has the fifth-best lottery odds, a half-game ahead of Philadelphia and two ahead of Toronto.

Keon Johnson had 21 points in place of Thomas, while Day’Ron Sharpe had nine points and 16 boards starting for Nic Claxton.

Kristaps Porzingis had 24 points and Jayson Tatum had 20 points, eight rebounds and eight assists for Boston.

The Nets fell behind early after a 24-5 first-half Celtics run. They trailed by 18 after Pritchard’s 3 capped the run.

The deficit swelled to 55-34 on a Tatum hook shot with 4:12 in the half.

The Nets had one last run in them, a late 13-5 blitz. Down by a dozen with 1 ½ minutes left in the third, Wilson’s 3 pulled it to 90-86 with 9:21 to play.

Maxwell Lewis (career-high 15 points on 6-of-7 shooting) made the most of his minutes, and his 3 cut it to 92-89.

Johnson hit a 3-pointer to make it 94-92, and another to get them within one in the waning seconds. But no closer.

“We’re just some dawgs,” Lewis said. “We’re underdogs, but we’re dawgs. Everyone tries to overlook us, and we’ll come at you. We’ll surprise you every time.”