The Celtics didn’t record a steal for nearly 45 minutes on Christmas. That last happened in 1990. Jaylen Brown saved them from an unseemly milestone. Then, he forced another turnover on Tyrese Maxey at half court trailing by five points, trying to prevent a second straight Boston loss —  Al Horford breaking loose for a dunk the other way — too little, too late. The Celtics revived their chance to stun a Sixers team on the verge of an upset with a last-second comeback. They couldn’t make any more mistakes. Instead, Joel Embiid, ailing from a pregame accident that hurt his ankle, beat Horford for a pair of free throws. Maxey, with less than two seconds left on the shot clock, torched the Celtics’ entire defense to the basket for a layup that put the game out of reach. Philadelphia won 69 seconds later, 118-114. “What I was thinking was, they’re not gonna get off Joel’s body,” Maxey said. “So if he set a good screen and I could curl it, I had a chance to make a layup.”