Chub Akpom opened the scoring in the first half before Cameron Archer added two more in the second half and Marcus Forss made it four in second half stoppage time.
Just before North End conceded the fourth, Bambo Diaby picked up a second yellow card and was sent off.
It was a bad day for the football but a good day for PNE fans who celebrated their annual Gentry Day, with 1,700 fans loudly backing their side throughout.
Unfortunately, the football did not match the backing, and this is how we rated the players on the day.
1. One down...
Preston North End's Bambo Diaby punches the ball after Middlesbrough score the opening goal Photo: CameraSport - Lee Parker
2. Freddie Woodman - 5
A shaky day for the PNE keeper who looked like he could do better with the third goal as Archer's strike wasn't in the corner. Kicking also a bit hit and miss. Photo: CameraSport - Lee Parker
3. Jordan Storey - 5
Over-committed for the second goal and Middlesbrough had a fair bit of joy coming down the left wing on the day. Photo: CameraSport - Lee Parker
4. Bambo Diaby - 4
It had all been going so well for Diaby but he had a poor game on saturday. His timing seemed to be off meaning he missed a few balls he would otherwise normally deal with, which led to his red card. Photo: CameraSport - Lee Parker