For the second straight game Luke Kennard made big shots for Duke. The sophomore's 3 with 4:45 left in the second half gave Duke its first lead, 73-70, since the end of the first. Tatum's 3 with 2:20 left made it 78-73 for the Blue Devils.
Deng Adel scored 21 points for fourth-seeded Cardinals (24-8), which led by a dozen with 13 minutes remaining. But Allen and Kennard took over down the stretch as Louisville struggled from the line.
Duke coach Mike Kryzyewski earned his 59th ACC Tournament victory to pass North Carolina's Dean Smith for the most in conference history.
The fifth-seeded Blue Devils (25-8) will play No. 1 seed North Carolina for the third time this season on Friday night at Barclays Center.
Brooklyn, NY. – Barclays Center
Friday, 7:00 p.m.
ESPN & ACC Network