The Jayhawks (2-1), coming off a loss Tuesday night to Michigan State, got off to a sluggish start against the Mocs, and still trailed 42-30 in the opening minutes of the second half.
Jeff Withey began their comeback with a basket inside, Johnson ripped a 3-pointer and McLemore slammed down the first of back-to-back highlight-reel dunks to trigger a 27-4 run over the next 12-plus minutes. Kansas merely had to go through the motions down the stretch to wrap up the win.
Farad Cobb was 6 of 7 from beyond the arc in the first half before finishing with 21 points for Chattanooga (1-1), the perennial Southern Conference contender. Z Mason added 13 points.
Kansas managed to extend the nation's third-longest home-court winning streak to 25 games despite having more turnovers (9) than field goals (8) in the waning minutes of the first half.
That's when things were still tenuous for the Jayhawks.
And when Cobb couldn't miss.
The freshman guard made his first 3-pointer in the opening minutes, and then after a miss, connected on five straight to finish off the half. Two of them came on consecutive possessions just before the break that helped lift Chattanooga to a 36-28 lead.
It was the Jayhawks' largest deficit at home to a non-conference opponent since 2005.
Kansas coach Bill Self, whose hallmark over the years has been gritty, in-your-shorts defense, was steaming on the sideline as he blew through just about all his timeouts trying to get Cobb to cool down. Several times he laid into McLemore and Jamari Traylor, his two freshman starters.
Chattanooga stayed hot early in the second half, getting 3-pointers from Mason and Ronrico White to extend the lead to 42-30. The Mocs were 10 of 16 from beyond the arc at that point.
That's when Kansas finally buckled down on defense, let loose on offense, and gave another packed crowd inside Allen Fieldhouse a reason to clamber onto its feet.
McLemore's first dunk during the surge prompted a timeout by Chattanooga coach John Shulman. After the Jayhawks forced a shot-clock violation when the game resumed, McLemore hopped on his pogo stick along the baseline and skied to grab a lob by Johnson for another dunk.
McLemore was on the giving end on the next possession, tossing up the pass for Releford to finish off a dunk, and Shulman frantically called another timeout.
Johnson's 3-pointer finally gave Kansas a 44-43 lead, its first since it was 2-0. McLemore added a breakaway dunk, Naadir Tharpe buried a 3, and Johnson connected with McLemore again for an alley-oop dunk. By the time Withey took a feed from McLemore for a dunk and then added a foul shot, the Jayhawks had suddenly built a 57-46 lead.
The Jayhawks cruised down the stretch from there, outscoring the Mocs 41-19 in the second half. They only committed four turnovers after the break.