Joe Mazzulla has no regrets about how the Celtics guarded James Harden in Game 1.

He left Al Horford on Harden. With the shot clock winding down, Harden stepped back from the 3-point line and nailed a 3-pointer to put the 76ers up by two with 8.1 seconds left and go on to win 119-115.

The 76ers’ decision to attack Horford in pick-and-rolls was one of their most successful plays of the night. 16 picks the 76ers set for Harden with the player covering Horford resulted in 28 points, spectrum per second.

Despite the 76ers’ continued success attacking Horford in pick-and-rolls with Harden, Celtics coach Joe Mazzola had no regrets about switching Horford over Harden for the game-deciding shot.

“Al is one of our best defenders. He has been all year,” Mazzola said. “[Harden] Made a big shot.”

Harden’s stellar shooting performance was the catalyst for the 76ers’ offense on Monday, shooting 50.6 percent from the field and 44.7 percent from deep. Those percentages are among the worst the Celtics have allowed in a game this season, as are Tobias Harris (18 points on 8-of-16 shooting), Tyrese Maxey (26 points on 10-of-24 shooting), and D’Anthony Melton. (17 points on 6-of-10 shooting) All chipped in.

Because of how well some of the 76ers’ other players shot, Mazzola didn’t think it was a good idea to double Harden any more than he did.

Asked about doubling Harden, Mazzola said it was a big catch. “That’s what you do on Harden: Do you want to try to throw an extra man on him? I called one in the first half and got the 3 open. [Georges] Niang and we did one again at the end of the third quarter and we gave one to Harris.

So, they had really good spacing and when they had shooters, they bound you. Will you get away from them? In the first half, we shifted a little bit more and gave up some catch-and-shoot shots to our role guys. Credit to them, they knocked them down.

Although the 76ers continued to hit shots because the Celtics didn’t double Harden in the second half, Mazzola believes they “adjusted well,” choosing not to play the results.

“We doubled up in the first half and they had six points off double teams on Harden. So, hindsight is always 20/20,” Mazzola said. “If we didn’t double it. [and they missed their shots], that would have been a very good defense. If we doubled it and they hit their shots, it would be, ‘Why did we double it?’ We doubled up twice in the first half on my call and they scored on it both times.