The Blue Devils (11-0) posted their second home blowout in four days in advance of their ACC opener this weekend at Boston College.
Marques Bolden (17 points), Wendell Carter Jr. (15), Grayson Allen (14) and Gary Trent Jr. (14) added to the scoring, while Javin DeLaurier and Alex O'Connell both scored nine points.
Bagley's 11 rebounds gave the freshman forward nine double-doubles. Bolden had 10 rebounds.
Duke had a 100-54 advantage with 8:32 to play, reaching the century mark for the first time this season after eclipsing 90 points six previous times.
Trent hit a pair of 3-pointers and Carter scored five points in Duke's opening 12-1 burst. Six minutes into the game, the margin grew to 26-5. The Blue Devils built a 30-point lead in just more than 10 minutes.
The 71-34 halftime score left the Blue Devils one-point shy of the team record for points in a half. Still, it topped Duke's largest halftime margin of the season -- that was set at 26 points Saturday against South Dakota.
Bolden, a sophomore center, matched his career high by halftime with eight points.
Duke had 12 offensive rebounds in the first half to the Red Flash's 13 total boards.
Jamaal King, Andre Wolford and Keith Braxton all scored 13 points for St. Francis (3-5), which has three of its last four games. Wolford, who made eight 3-point baskets in a two-point loss Saturday at Stony Brook, was 4-for-11 from long range.
NOTES: This marks the 134th week that Duke holds a No. 1 ranking, matching UCLA for the most of any Division I men's team. ... Duke G Grayson Allen played in his 50th victory at Cameron Indoor Stadium. ... This was the first meeting between Duke and St. Francis. ... This marked the second time St. Francis has faced a top-ranked team, losing to Notre Dame in January 1974 the other time. ... In St. Francis' first two victories this season, the Red Flash allowed 56 and 54 points, so Duke topped those marks in the first half. ... Duke's next game comes Saturday afternoon with its Atlantic Coast Conference opener at Boston College. ... St. Francis goes to Niagara on Saturday.