After a goalless first half, Amad put the visitors ahead with an excellent strike into the top corner.
Substitute Alex Pritchard then added a second before Jack Clarke completed the scoring with a low effort.
After Millwall failed to beat Blackburn, Sunderland moved into the top six and will now face Luton in the play-offs.
Here’s how Phil Smith rated the Sunderland players against Preston:
5. Dennis Cirkin - 6
Had a steady first half defensively with only a couple of opportunities to really break forward. Was replaced at the break by Alex Pritchard with his side needing to find a goal. The left back had also taken a nasty blow to the ankle in the first half. 6 Photo: Frank Reid
6. Dan Neil - 8
Snuffed out some hugely dangerous counters in the first half and was there to protect his side in the second as they began to cut through Preston. A hugely accomplished performance. 8 Photo: Martin Swinney
7. Pierre Ekwah - 9
Mowbray’s patient work in introducing him to the side and working on his physicality is paying off handsomely. He was absolutely dominant here, clever on the ball and untouchable off it. What a find. 9 Photo: Frank Reid
8. Patrick Roberts - 8
Cut through Preston time and time again in the second half, didn’t get on the scoresheet but was a big part of the result with another dazzling exhibition of dribbling. 8 Photo: Martin Swinney