CLEVELAND -- A game after the Cleveland Cavaliers dominated the Boston Celtics to take back control of their perch atop the Eastern Conference, the Cavs once again devolved into a group with more questions than answers. Friday's 114-100 loss came against an Atlanta Hawks team that was resting all five of its starters.

"Obviously a bad performance," Cavs coach Tyronn Lue said after his team failed to protect a nine-point lead midway through the third quarter and fell behind by as many as 20 in the fourth. "Beat Boston and have the game that we had, and to come back and not validate it against a team that didn't even play their guys.

"I didn't think we respected them tonight. I thought we thought we'd just mess around with the game until it was time to knuckle down. By that time, they already had confidence. That's who we've been. That's who we are. I hate it.

"These games like this come back and bite you, especially down the stretch when you're trying to get some rest. Trying to hold on to that No. 1 seed and getting rest, and you come out and have a performance like this, it's not good."

One Cavs source told ESPN it was the "most embarrassing loss of the season by a lot." Another told ESPN, "I saw it coming," when he got wind of the Hawks sitting their marquee guys. Yet another told ESPN of the Cavs' up-and-down nature, "I don't get it. I don't f---ing get it."

"I didn't think we respected them tonight. I thought we thought we'd just mess around with the game until it was time to knuckle down. By that time, they already had confidence. That's who we've been. That's who we are. I hate it," coach Tyronn Lue said. Ken Blaze/USA TODAY Sports

Cleveland still holds a one-game lead over Boston for the No. 1 seed with three games to play, but Friday's result clearly rattled the defending champions.

"We needed it tonight," said Kevin Love, alluding to the fact that a win would have put Cleveland in the driver's seat to rest its stars down the stretch while still clinching the No. 1 seed. "It was a huge, huge game for us, and we lost. That's the most frustrating, most disturbing and it sucks."

LeBron James had his usual dominant stat line -- 27 points on 12-for-15 shooting, 8 rebounds, 7 assists and 2 steals in 41 minutes -- but it wasn't enough to thwart the Hawks' 29-7 run in the fourth quarter that changed the game.

"As a group, our energy was very low," James said when asked for an explanation for the outcome. "I have no idea why, but it was just low."

James finished the game sitting on the baseline, removed from his teammates on the bench. While the four-time MVP took a cautious approach to digesting the Boston win on Wednesday, saying, "We'll see," when asked whether it would be the catalyst the Cavs were searching for, he did expect more than what Cleveland showed against a Hawks team that was without Paul Millsap, Dwight Howard, Dennis Schroder, Kent Bazemore and Thabo Sefolosha.

"You expect for us to want to get better, and we were doing that and we took a couple steps back tonight," James said.

Adding injury to insult, Kyrie Irving came away from the game with concerns about his surgically repaired left knee.

"After halftime my left knee just started kind of flaring up," said Irving, who finished with 18 points and seven assists. "[Thursday] just was a terrible day for me and my knee. ... It was just one of those days. Guys that have had knee surgery before understand that. It was one of those days. I just did my best all of yesterday just trying to recover and do everything possible. So I had a great chance of playing at a high level, and then after halftime it just f---ing flared up. Excuse my language, sorry."

Lue could have went with "sorry" to describe his team's effort. He chose "stupid" instead.

"Just stupid, man," said Lue, who compared the loss to others in the past when the Cavs fell flat against undermanned opponents (Memphis last season; New Orleans this season). "It's tough because as a coach you're searching and trying to get the right guys out there to bring some energy. Guys have been playing 38 and 39 minutes, and Bron, you know, he seems to have the energy every single night. A lot of times guys are not picking that up. Tonight is where we needed guys to pick up the energy and pick up the slack. We just didn't do it."

Cleveland's bench was outscored 55-21, with former Cav Mike Dunleavy, traded for Kyle Korver at midseason, doing most of the damage as he scored 20 points on 6-for-9 shooting.

"I just know we didn't respect those guys," Lue said. "Dunleavy comes off the bench and scores 20 points. We know what he does, he shoots the basketball. We're late getting to him, late chasing him off screens. Late on a lot of screens. They came in, they played hard and they beat us."

With the playoffs just a week away, James was asked whether the Cavs can simply throw away the Hawks game and regroup.

"I mean, do you have a choice?" James said. "You don't have a choice. We got three more games left, I believe -- Sunday, Monday, Wednesday. We don't have a choice. We move on to the next one and try to get better from there."