I have heard a lot of Celtics doubters say something along the lines of "Porzingis won't play that well again", but I am not sure I buy that. He averaged 20 pts/7 rebs in the regular season in about 30 min. Game 1 he had 20 pts and 6 rebs. He probably isn't going to play as well as he did in the first half for a whole game, but if you look at this in aggregate, for the whole game, it is not surprising or an outlier.
The other thing is that this was his first game back after missing 5.5 weeks. Logic says that he will be better in Game 2 than Game 1, and maybe better Game 3 over Game 2, not worse. If he has some sort of injury set back, that is different, but there is no indication of that. He looks fine.
If people are putting their hopes in Porzingis not scoring 20 points every game, as a way that the Mavs can get back into this, I think that may be flawed logic. He may play more evenly over the course of a game, vs. having a really hot quarter, but the result or the impact on the game is the same.