Porzingis is not very good at basketball.
He's forced a few offensive rebounds second possessions for his team in the fourth, but he's also had turnovers, badly missed shots, and stalled offensive possessions as he shoots fade away 18 footers over players a foot shorter than him.
If you notice Morris' three three pointers in the fourth, that was also on Porzingis. He was the weakside man that over-rotated and did not have the speed to stunt or recover. Great coaching by Lue. Some coaches isolate bad defenders by forcing switches on an island against great scorers. Lue (or Rondo or Leonard) isolated Porzingis on the weakside and blew the game open with wide open looks.