An alley-oop dunk by Bell with 4:16 left stretched Missouri's lead to 73-62, and the Tigers led comfortably the rest of the way.
Pressey added 17 points for the Tigers after making only 3 of 14 shots from the field in the first half, including 1 of 6 from 3-point range. After a missed jumper with 1:10 remaining in the first half, Haith quickly turned his back to the court and slapped his hands in the first of many signs of frustration with his team.
Haith said he needed to remind Pressey to remain poised, as well as saying the junior guard doesn't need to be the team's entire offense.
"Teams are going to make shots; people are going to make shots," Haith said. "And I thought we rushed things. And Phil's got to get better at that. Just in terms of the trust factor.
"There may be a night where we want Phil taking 18 shots, but that's not his game right now."
Previously saying his team struggled with slow starts in its first two games of the season, Bowers said energy wasn't the problem Tuesday night. Rather, mental focus and lack of execution may have been the culprits.
Bell added 12 points and 11 rebounds for Missouri after coming off the bench for the third consecutive game. Bell's averaged 12 points in those three games while playing 26.3 minutes, an increase of 4.3 per game from when he was starting.
Haith has asked Bell to become the team's best perimeter defender, rather than being the team's leading scorer, as the Pepperdine transfer is used to being.
"I've always had the potential to be an excellent defender," Bell said. "I still haven't reached that potential yet, but I believe that I made steps in the right direction."
The Tigers moved to 7-0 all-time against Southeast Missouri.