Classmate Andres Sandoval chipped in 15 points and sophomore London Warren added 11 in his first start of the season for UD (15-4, 3-3).
The efforts of Sandoval and Warren were enough to compensate for the absence of forwards Charles Little and Chris Wright, both rehabbing injuries.
Tommie Liddell III led the Billikens (11-9, 2-4) with 10 points.
After falling behind early, the Flyers used a 10-0 run midway through the first half to build a 19-14 lead they did not surrender. During the run, Roberts connected on a pair of three-pointers to ignite the sold-out crowd of 14,435.
The Flyers extended their lead with a 9-2 run to end the first half. Warren scored all nine of Dayton's points during the run, as the UD lead stretched its lead to double-figures for the time heading into halftime, 28-18.
The Flyers caught fire in the final 20 minutes, led by Sandoval. He scored 13 of his 15 in the second half to help Dayton outscore SLU 35-18 after halftime.
Sandoval shot 3-of-7 from three-point range to pace Dayton's attack. Overall, the sharp-shooting Flyers connected on 8-of-17 from beyond the arc and 7-of-7 from the foul line, while the Billikens shot just 37-percent from the floor to finish with their fourth effort of 40 points or less this year.
Dayton swept the season series with Saint Louis winning the first matchup on Jan. 12 in St. Louis, 68-57 in overtime.
Wednesday's win was Dayton's first since Little was sidelined after breaking a bone in his right foot against UMass on Jan. 16. Little was once again joined in sweats by Wright, the team's second leading scorer and top rebounder, who continues to recover from ankle surgery.