Marshall didn't miss a shot, going 6-for-6 from the field, 3-for-3 from the free-throw line and drained both of his three-point attempts. He has scored in double digits in six straight games dating back to last season and entered the game averaging 16.8 points.
Grambling State (0-3) led briefly in the first period, but Marshall tied it at 4 with a layup, then drained a 3-pointer to give the Bears (3-0) a lead they never relinquished.
Missouri State shot 59.6 percent from the field on 34-of-57 shooting, compared with 38.6 percent for the Tigers on 22-of-57 shooting.
Former Kentucky guard Ed Davender, the only Wildcat with at least 1,500 points and 400 assists, has died. He was 49.
Guard Naz Mitrou-Long, whose 2015-16 season ended in December due to hip problems, has been granted a hardship waiver for the coming season, Iowa State said.
As the Sooners look to life without superstar Buddy Hield and his sidekicks, it's clear their unseasoned players will need to grow up fast.