A lot of things went wrong for the Boston Celtics in Game 1 of the Eastern Conference Finals against the Miami Heat, but for Jayson Tatum it all boils down to one major mistake: defense.

Speaking to reporters after their 123-116 loss at home, Tatum admitted that they couldn't allow the Heat to score 46 points in a quarter. For those who missed it, Miami couldn't miss in the third quarter as they turned the game around with a 46-25 run. In just 12 minutes, the nine-point lead that Boston built in the first half disappeared.

“We just gave up 46 points in the third, so it’s defense and transition and offensive rebounds and not closing out to shooters. Those are some things that we really gotta focus on and go over tomorrow in practice,” Tatum said of their loss, per Jared Weiss of The Athletic.

Sure enough, it's hard to argue with that. Aside from that horrible showing in the third, the Celtics won all other quarters. Unfortunately, even that was not enough to get them out of the hole they dug in the third. They simply cannot allow Miami to get their offense going and have that much confidence.

As Celtics fans would say, however, defense isn't the only issue for Boston. Offense was nowhere to be found for the team as well, with Jayson Tatum being one of the major culprits. In difficult situations, he should be the one to step up. Nonetheless, he went MIA in the second half for the team.

Tatum scored 12 points in the second half, but eight of it were from free throws. He even went 0-of-3 from the field in the final quarter. Aside from failing to make a shot, he lacked aggressiveness on the offense as well.

Boston surely needs to review the film of the game to determine all the mistakes they made. If not, they could be in trouble come Game 2.