Rodney Chatman scored 17 points. Obi Toppin scored a season-low eight points.
Dayton shot 51.9 percent from the field and held Grambling State to 32.3 percent. Each team had 12 turnovers. The Flyers had a 39-30 rebounding advantage.
Dayton returns to action at 7 p.m. Dec. 30 against North Florida at UD Arena. That will be the last non-conference game.
Dayton postgame press conference: Grant after Grambling game
The Flyers took control with a 13-0 run early in the first half and led Grambling State 40-22 at halftime/
Watson led Dayton with 17 points on 5-of-7 shooting. Rodney Chatman scored 12 on 5-of-8 shooting. Obi Toppin scored six points. He dunked in the final seconds of the half.
» COLORADO GAME: Grant says it’s a tough loss to take | Photos of Flyers vs. Buffaloes
Grambling State, one of the three teams on Dayton’s non-conference schedule that ranks among the bottom 75 teams in the Ken Pomeroy ratings, hung with Dayton for about three minutes.
Seven straight points by Watson broke a 6-6 tie and gave Dayton a 13-6 lead at the 14:27 mark. Dayton led by as many as 19 points in the half.
Dayton shot 52 percent from the field. Grambling shot 32 percent.
NOTES: Jalen Crutcher missed the game. He's in concussion protocol after a hard fall against Colorado. ... Chase Johnson missed his fourth straight game with an illness.