Dave McMenamin of ESPN passed along postgame reaction from the 39-year-old coach, who's unhappy with the identity the Cavs have developed with the playoffs on the horizon.
"I didn't think we respected them tonight," Lue said. "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."
He called it a "bad performance" and added: "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."
Atlanta, which currently sits fifth in the Eastern Conference, was without several key contributors for the contest, including frontcourt tandem Paul Millsap and Dwight Howard. The makeshift group shot 50.6 percent from the field and knocked down 16 threes to pull off the upset.
Superstar forward LeBron James admitted the Cavs never found a spark against what amounted to the Hawks' second and third units, per Joe Vardon of Cleveland.com.
"As a group our energy was very low," he said. "I have no idea why, but it was just low."
The loss leaves the Cavaliers just one game ahead of the Boston Celtics for the top seed in the East. They failed to consolidate their two-game advantage following a head-to-head victory over their closest conference rivals Wednesday night.
Cleveland gets an immediate opportunity to right the wrong when it faces off with Atlanta in a rematch Sunday afternoon. James and Co. will need to play far better since the Hawks should be much closer to full strength for the second clash.