I've never really liked Dallas' offense during the playoffs. It's very heliocentric and reliant on Luka (and to a lesser extent, Kyrie) to make something happen with everyone else standing around in designated spots. The game last night was really just hoping Luka makes some tough shots. When Dallas' went on their run in the third quarter it was really because Luka made a series of extremely difficult shots, and that just isn't sustainable over the course of the game.
It's funny to see how so many people were suckered into talking about individual offensive ability leading up to the series, which led to a ton of focus on "How will the Celtics stop Luka/Kyrie?" and then you watch Game 1 and it's clear the Celtics have a far superior offense because they play five out, everyone moves, and they really swing the ball around to the open man. Luka is the best offensive player in this series from an individual skill perspective, but the Celtics are better at actually putting the ball into the basket than the Mavericks, and that is what matters.
A hugely impressive thing to me was how the Celtics schematically took away Dallas' lob game, which had devastated teams during this run. I don't recall any successful lobs and only a few attempts from the Mavs. That really reduces the effectiveness Lively/Gafford have on offense.
Porzingis' contributions on defense were just as important as his shot making on offense. The Celtics did get carved up at the rim by Indiana, but KP is such a deterrence with his length and timing--he made a bunch of plays in the first half, some of which were highlight blocks and others were just him effecting shots at the basket.