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:
1. Anthony Patterson - 7
Distribution was good, as was his command of his box. Made one huge save seconds after Sunderland took the lead, which was a big moment in the game. 7 Photo: Martin Swinney
2. Lynden Gooch - 7
Tenacious in the first half as Preston started brightly, and then made a good go of playing on the left of a back three before Mowbray went for the more orthodox option in Joe Anderson. 7 Photo: Frank Reid
3. Trai Hume - 8
Recovered from a slightly shaky start to produce another very strong performance in the heart of defence. Good off the ball and tidy on it. 8 Photo: Frank Reid
4. Luke O’Nien - 8
Produced another excellent performance in the heart of defence, particularly in the second half when he had to withstand a lot of pressure as the game broke wide open. 8 Photo: Frank Reid