Kyron Cartwright and Rodney Bullock added 13 apiece for the Friars (20-12).
Marcus Foster had 19 points and Davion Mintz added 14 for Creighton (21-11).
After Foster missed a 3-point attempt with 1 minute, 23 seconds left in overtime, Providence's Isaiah Jackson made two free throws to give the Friars a four-point lead, the biggest advantage either team had gained since 12 minutes in regulation.
Creighton cut the lead to two with 12 seconds left on a pair of Mintz free throws, and Diallo hit a free throw with eight seconds left to give Providence a three-point lead, but Mitch Ballock missed a 3-point attempt with one second left and the Friars advanced to Friday's semifinals matchup against Xavier.
Foster missed a potential game-winning 3-pointer with one second left in regulation after Diallo grabbed the offensive rebound of his own missed jumper and made a layup to tie the game at 59 with 13 seconds left.
Neither team led by more than three for the final 13 minutes of the game, and neither team led by more than two for the last 7 minutes, 50 seconds of regulation.
The Bluejays shot 42.4 percent from the field compared to the Friars' 36.9 percent. Providence owned a 45-39 advantage on the boards and dominated the offensive glass 16-7. Diallo did most of the damage with four offensive rebounds, but Jalen Lindsey added 10 rebounds to go with his 11 points.
Jackson had an important nine points off the bench to help the Friars' effort, but he shot just 2 for 9.
Ballock had 12 points for Creighton, Jacob Epperson had nine points off the bench on 4 for 5 shooting, and Khryi Thomas had eight points but committed five turnovers.
--Field Level Media
Providence | Creighton | |
Alpha Diallo 19 | Scoring | Marcus Foster 19 |
Alpha Diallo 3 | Assists | Davion Mintz 6 |
Jalen Lindsey 10 | Rebounds | Toby Hegner 7 |
Alpha Diallo 5 | Free Throws Made | Davion Mintz 6 |
Kyron Cartwright 2 | Steals | Khyri Thomas 4 |
Rodney Bullock 3 | Blocks | Jacob Epperson 5 |
Team | Points | FG% | 3PM-3PA | FTM-FTA | Assists | Rebounds | Blocks | Steals | Turnovers |
Providence | 72 | 36.9 | 5-22 | 19-31 | 8 | 39 | 3 | 8 | 11 |
Creighton | 68 | 42.4 | 6-23 | 12-18 | 16 | 34 | 7 | 6 | 13 |