Lacy's total on 18 carries was a career high.
T.J. Yeldon rushed for 144 yards with two scores as the Crimson Tide (6-0, 3-0 SEC) roared back from a bye week with a one-sided win.
AJ McCarron was forced to play with a knee brace after a third-quarter sack but shook off the injury to complete 16-of-21 passes for 171 yards in a game that was halted for 38 minutes due to lightning.
The Tigers (3-4, 0-4) got only 126 yards on 12-of-29 passing from Corbin Berkstresser, who was intercepted twice.
Missouri fell to 0-13 all-time against No. 1-ranked teams.