Looking at the box score doesn’t fully tell the story of what the Celtics did in Game 1 of the NBA Finals Thursday night.

They missed a lot of free throws. They had more turnovers than Dallas. After a sizzling start from 3, they cooled way off. Jayson Tatum scored only 16 points, although he finished with a team-best +21.

Didn’t matter. They built the largest first-quarter lead in NBA Finals history (17 points), extended that to as much as 29, and withstood a slight Dallas rally that cut the margin to as close as 8 in the third quarter before wrapping up a 107-89 victory.

Game 2 is Sunday night at the Garden.

Dallas fell to 1-6 in Game 1s under Jason Kidd. What the Celtics will need to be on guard for now is how Dallas responds, because the Mavs have won 4 of 6 Game 2s under Jason Kidd.

The eye test saw a dominating Celtics performance in Game 1. The C’s looked exactly like the team that waltzed through the regular season and the Eastern Conference playoffs. Kristaps Porzingis looked like the unicorn he was described as while in New York, never was in Dallas, and blossomed into in Washington before joining the Celtics.

Dallas was always going to have trouble with that Porzingis. Mavs centers Daniel Gafford and Dereck Lively II cannot hang with the Celtics big on the perimeter. Attempts to switch off with smaller defenders to pester KP failed spectacularly. His 20 points, 6 boards and 3 blocks in 21 minutes were decisive.

Sunday will likely be a tougher test for the Celtics, who have a 1-2 mark in these playoffs in Game 2s. That history, as well as the fact that they allowed the Mavs to briefly get back in the game despite a terrible showing by Kyrie Irving and a bad shooting night (7-27 from 3, 12-19 at the line), gives Celtics boss Joe Mazzulla a lot to harp on before Sunday night.

The Celtics got away with dropping Game 2 to an outmanned Miami team, and got away with a Game 2 loss to the soon to be depleted Cavaliers. Against Indiana, the Pacers were in three games in crunch time but the Celtics’ superior team handled their business.

The good feeling from Game 1 is a warm embrace that will last until tipoff Sunday. Then the Celtics need to have an even better showing. They want to go to Dallas next week with the Mavs desperate. They must hold serve.

Boston can win with a similar offensive showing, but have to lock down on defense and not allow Irving or other Mavericks to get going. The C’s outscored Dallas by 27 from distance; pretty significant disparity in an 18-point game. A few more makes by Dallas and a few more misses from Boston is not out of the question, so the margin for error isn’t massive. Best not to go there.

After Minnesota knocked off defending champion Denver in the WC semifinals, recency bias had Anthony Edwards being compared to Michael Jordan. Dallas handled that, then became the next hot thing. Boston handled that in Game 1.

Now they have to do it in Game 2. No slip-ups.

Jayson Tatum #0 of the Boston Celtics dunks in-between Maxi Kleber #42 and P.J. Washington #25 of the Dallas Mavericks during the second quarter of Game 1 of the NBA Finals at the TD Garden. (Photo By Matt Stone/Boston Herald)