Duke's Grayson Allen, who poured in 17 points in the opening 10 minutes, finished with 23 points.
Duke closed the regular season by winning five of its last six games. This was its postseason opener and just like in last year's tournament title game, it defeated the Fighting Irish.
Second-seeded Duke (26-6) meets 12th-ranked North Carolina in Friday night's second semifinal.
Bagley, who ripped down 17 rebounds, made 15 for 23 from the field in the first game since being named ACC Player of the Year. Allen went 5-for-6 on 3-point attempts. Trevon Duval of Duke supplied 11 assists.
Bonzie Colson's 18 points, Martinas Geben's 14 points and Matt Farrell's 11 points and 12 assists led 10th-seeded Notre Dame (20-14), which shot 5-for-23 from 3-point range.
The Fighting Irish went 3-2 in five games since Colson returned from about a two-month absence with a foot injury. Notre Dame won the previous two nights to bolster its NCAA Tournament credentials before running out of steam.
Duke opened a 53-41 lead with a strong start to the second half.
Duke led 41-37 at halftime despite only one field goal across the final six minutes. The Blue Devils went 2-for-14 from the field to close the half.
Allen had 12 points in Duke's opening stretch for a 25-17 lead, including back-to-back 3-pointers to close the run and make him 4-for-4 from long range in the opening seven-plus minutes.
Allen's fifth 3-pointer made it 32-19.
Notre Dame, which rallied from a 21-point second-half hole a night earlier against Virginia Tech, stormed back to pull within 37-31 as Duke forward Wendell Carter Jr. picked up his third foul. Four consecutive Notre Dame missed free throws prevented it from becoming closer.
--Field Level Media
Notre Dame | Duke | |
Bonzie Colson 18 | Scoring | Marvin Bagley III 33 |
Matt Farrell 12 | Assists | Trevon Duval 11 |
Bonzie Colson 9 | Rebounds | Marvin Bagley III 17 |
Martinas Geben 2 | Free Throws Made | Grayson Allen 4 |
Bonzie Colson 3 | Steals | Grayson Allen 1 |
Bonzie Colson 1 | Blocks | Javin DeLaurier 2 |
Team | Points | FG% | 3PM-3PA | FTM-FTA | Assists | Rebounds | Blocks | Steals | Turnovers |
Notre Dame | 70 | 44.8 | 5-23 | 5-11 | 25 | 26 | 2 | 7 | 7 |
Duke | 88 | 55.4 | 8-17 | 8-12 | 21 | 38 | 4 | 5 | 10 |