Mason Plumlee added 10 points and 11 rebounds for the second-seeded Blue Devils (28-4), but league player of the year Smith sustained an apparent toe injury with under 7 minutes left.
The two-time reigning ACC tournament champions held Maryland without a field goal for 6 minutes down the stretch to reach the conference semifinals for the fourth straight year.
Jordan Williams had 16 points and 16 rebounds to lead the seventh-seeded Terrapins (19-14). They kept things tight for much of the second half, pulling to 63-60 on Dino Gregory's layup with 10:15 remaining.
Singler hit a driving layup with just under 9 minutes left to start the decisive surge. Duke reeled off nine straight points, outscored Maryland 11-1 over a 4½-minute span and rode a 24-9 run to an 18-point lead in the final minute.
But without question, the biggest concern for the Blue Devils was the condition of their star guard's foot.
Smith, the 14th Duke player to win the conference's top award, was hurt with 6:48 left when he planted in the lane and tried to jump, but instead lifted his leg off the ground and fell to the court. He did not return.
There was no immediate word on the severity of the injury, which couldn't help but evoke memories of the toe injury that has kept freshman point guard Kyrie Irving out for the past three months. Coincidentally, Irving was seen jogging, shuffling and shooting around about 90 minutes before tipoff in uniform shorts and sneakers. He was dressed in street clothes and topsiders for the game.
Smith was having a rough night before he was injured. He missed his first seven shots and finished with seven points on 2-of-11 shooting with five turnovers and only two assists.
Singler picked up the slack for his fellow senior, hitting 10 of 15 shots to finish one point shy of his career high. Seth Curry converted a momentum-building three-point play during the run.
Kelly, who earlier in the season made 18 consecutive shots over a four-game span, had a near-perfect shooting night — hitting all five of his attempts from the field but missing his only try from the free-throw line.
Kelly's 3 with 3½ minutes left broke a 31-all tie and started Duke's 11-2 run that closed the half. Singler's drive down the lane with 4 seconds to go gave the Blue Devils their largest lead, 42-33, at the break. But for the first 30 minutes, the Terrapins never let them pull too far ahead. They scored on 14 of their first 16 possessions of the second half to keep it tight.