The Boston Celtics' season will effectively come to a close after suffering a brutal 128-102 loss in Game 3 to the Miami Heat.

While the C's came into the playoffs with high hopes, the Heat have proven to be a much more complete and mentally tough team. And even though the Eastern Conference Finals are technically not over, no team in NBA history has ever come back from a 3-0 series deficit.

Plus, right now Boston doesn't look capable of making a run. Its offense is sputtering and the defense has been even worse. Simply put, Game 3 was an absolute disaster in every way (and that's putting it nicely).

So what went wrong for the Celtics? Well, just about everything. However, let's condense it and look at three major takeaways from Boston's potentially season-ending Game 3 loss to the Miami Heat.

3. Jayson Tatum and Jaylen Brown let the Celtics down

2023 All-Stars Jayson Tatum and Jaylen Brown are supposed to be the best players on the Celtics. Yet, they arguably played worse than all of their teammates in Game 3.

Brown has performed terribly all series and on Sunday night he put up just 12 points while going a putrid 6-for-17 from the field. He also missed all of his 3-pointers (0-for-7), had three turnovers, and posted the worst plus-minus rating of the entire game (minus-25). It was a catastrophe for the 26-year-old, as he lost his touch after the first quarter and started to force some terrible shots down the stretch.

To make matters even worse, Tatum wasn't much better. He dropped 14 points while shooting a dismal 6-for-18 from the field. He had three turnovers, shot 14% from deep, and had the second-worst plus-minus rating of the night (minus-23). Tatum hasn't been awful this series, but his Game 3 performance was by far his worst.

Your star players aren't going to play well every night, however, they should never be your worst guys on the floor. Tatum and Brown looked frustrated and seemed to give up later in the contest. For a team with championship aspirations, that's extremely disheartening.

2. Boston's defense from last year is officially gone

The C's played their worst defensive game of the playoffs (and perhaps the season) during Game 3. They let up 128 points and allowed Miami to shoot an incredible 56.8% from the field. The Heat were getting open shot after open shot and made Boston pay for it time after time.

What's most frustrating about this is that Miami star Jimmy Butler looked somewhat human on offense. He had 16 points on 5-for-13 shooting, and while he facilitated the ball well, he wasn't connecting on everything like he's done in the past. Instead, Miami's bench and role players cooked Boston. Five of Butler's teammates were in double-digits, and Duncan Robinson and Gabe Vincent combined for a whopping 51 points.

It's hard to believe this Celtics squad shut down the reigning MVP last series and prided itself on defense last season. Whether it was double teams or a porous zone defense, the C's just couldn't slow Miami down with any scheme.

1. The Celtics look like a team ready to be done

To add to the disappointment from Game 3, at times the Celtics appeared to be checked out. They dropped the lead to 13 points at the start of the third quarter, but then after that, they let up a few more triples and broke down. It didn't seem like the Green Team had any fight left in them at that point.

With the season on the line, you'd expect a talented team to come out of halftime ready to cut into a big lead. Instead, the Celtics sleepwalked through the second half and gave in.

Whether this effort issue stems from the stars, the coaching, or the entire team isn't crystal clear, yet if the C's play like that again their 2022-23 campaign will be officially over. Game 4 will be in Miami once again on Tuesday night, as the Celtics will have to snap out of their daze to try and extend their season.