Darius Days scored 16 points and Efton Reid had 12 points. Reid made all six of his field-goal attempts in his first double-digit scoring effort against an SEC opponent and his highest point total since Dec. 22.
Xavier Pinson, a transfer from Missouri, and Eric Gaines added 11 points each for #5 seed LSU (22-10), which will face #15 Arkansas, the fourth seed, in the quarterfinals Friday afternoon. Arkansas won both regular-season meetings with LSU.
DaJuan Gordon scored 19 points, Trevon Brazile had 15 and Javon Pickett added 14 to lead #12 seed Missouri (12-21), which defeated 13th seed Ole Miss 72-60 in the first round Wednesday night.
Kobe Brown scored five points as Missouri started the second half with a 10-4 run and pulled within 43-33.
Reid had six points and an assist during a 14-2 run that gave LSU a 57-35 lead.
LSU, which last month scored the first 15 points of the second half to take control in a 75-55 victory over Missouri, had a strong start to the first half this time. Pinson scored seven points and Days had five as LSU took a 12-2 lead.
Brown's two layups provided Missouri's only points during the first eight minutes. Eason scored five points and Days added a 3-pointer as LSU expanded the lead to 30-8.
Even while smothering Missouri with its defense, LSU did not commit a foul until 7:47 remained in the first half.
LSU's scoring pace slowed, but Eason's jumper still pushed the lead to 34-9 before Missouri had its best offensive stretch of the half. Gordon made two 3-pointers and Ronnie DeGray III made one to pull Missouri within 34-18.
Pinson's two free throws ended Missouri's 9-0 run and LSU held a 39-23 lead at halftime.
LSU scored 21 points off Missouri's 15 first-half turnovers.