Sunday's matinee matchup with the Boston Celtics was meant to be a final litmus test for the Cleveland Cavaliers for what many are anticipating could be an Eastern Conference Finals matchup. 

The second half of the contest lived up to the billing, but it was the sloppy first half for the Wine and Gold that wound up costing them what would have been a statement victory with just 19 games to go in the season. 

What went wrong? Here's what stood out about the Cavs 109-98 loss to the Celtics: 

Jarrett Allen's knee injury isn't expected to be serious, but he was unable to go against Boston on Sunday. That left Kenny Atkinson with a spot to fill in the starting lineup and he rolled with Sam Merrill to combat the Celtics wing heavy lineup. 

In full, the starting lineup featured Donovan Mitchell, James Harden, Evan Mobley, Dean Wade and Merrill. The first sub in was Jaylon Tyson for Mitchell around the five-minute mark. It provided a glimpse into how Atkinson may deploy certain guys in a potential playoff series with Boston in the coming months.

Clearly, he likes Wade for his ability to defend a Tatum or Brown. Merrill would probably be one of the first guys off the bench for his shooting ability along (granted he had a miserable day at the office in this one). Tyson will is sure to remain one of the first guys in as well for his prowess on both ends. 

The Cavaliers played an all-time bad second quarter on Sunday afternoon. It took Cleveland five minutes to score its first bucket of the stanza (a Mobley dunk), going more than seven minutes without a made field goal in the process. That stretch to open the second included five total missed shots and four threes. 

It only got worse from there and when the quarter mercilessly ended the Cavs had gone 4-of-25 from the floor, including a brutal 0-of-14 from three. It was about as bad a shooting quarter a team has ever had. 

When the Cavs made the blockbuster trade to send Darius Garland to the Clippers for James Harden, it was for games like this. Unfortunately, this one didn't go so well for the 36-year-old. 

Sure, he finished with 18 points and made a handful of big shots and plays down the stretch as Cleveland tried to scratch and claw its way back into it. But it was too little too late. Harden was just 6-of-16 from the floor and in moments earlier on when the Cavaliers needed him, he went ice cold. 

The 10 assists were huge, but they needed a little more from their deadline acquisition on Sunday. 

One thing that really stood out from the Cavaliers offensive struggles was just how difficult the Celtics made it on the defensive end. Atkinson talks a lot about trying to get guys to "their spots." That felt nearly impossible in this one. 

The Cavs tried to get to the paint. They had actually outscored the Celtics in the paint in the first half and for the game, but on too many occasions to count, Boston denied guys from getting to the spots they wanted.

That left Cleveland shooting a lot of threes (i.e. the second quarter) and while making a few more certainly would have helped, it's hard to beat Boston in a three-point shooting contest. 

As bad as thing were for the Cavs offensively at times, defensively, they absolutely met the moment of this game. That second quarter was a perfect example of that. While Cleveland stumbled their way to 10 points, conversely, it held the Celtics to just 21 points in the same stanza. Had they made even a few shots, the game could have gone totally different. 

The defensive effort was relentless all the way through. They forced 11 turnovers, blocked six shots and forced plenty of tough shots. Boston just has too many guys who can make those shots, especially from three. 

The commentary around Mobley's first few games back from the calf injury was hyperbolic. Now that he's played a handful of games he's looking like the dominant player he was before the injury again. 

Sunday was no different. Mobley set the tone early, scoring the first seven of Cleveland's 11 points. He had several clutch plays down the stretch as the Cavs mounted a fierce comeback. 

As the primary five, he blocked three shots, snagged eight rebounds. He was dominant on defense and matched it on the offensive end with 24 points on 10-of-19 shooting. If that Mobley shows up consistently, the Cavaliers ceiling his very high. 

It's unfair that the Celtics are as good as they are and now get to add Jayson Tatum BACK into their lineup the rest of the season. They're honestly a better team because they were missing him for the first five months of the season. 

For most teams, when their best player takes a breather, it's fair to expect some regression, but because Boston learned how to play at a high level without him, they really don't miss a beat when he sits. 

By the way Tatum only shot 6-16, and still scored 20 points in his second game back from a ruptured Achilles. By the team these two teams potentially meet in the playoffs he's going to be more himself, which is also a scary proposition.