United manager Ole Gunnar Solskjaer fielded a mix of youth and experience in his first line-up of the new campaign, with Tom Heaton handed a second debut for the club after his return from Aston Villa.
United went ahead thanks to an interception and scrambled goal scored by Tahith Chong. The Holland U21 winger has signed on-loan with Birmingham City, though is doing his preseason training with United.
The visitors went further ahead through Facundo Pellistri, who struck after a superb through ball produced by fellow youngster Shola Shoretire.
Veteran Derby striker Colin Kazim-Richards hit a superb late goal for the hosts after a United pass was intercepted. Kazim-Richards collected the ball and fired his long range effort past Lee Grant in United's goal.
Here we have some of the best images from a sunny day at Pride Park:
Rooney was happy to welcome his old club to Pride Park - including former teammate Ole Gunnar Solskjaer.
Former United FA Youth Cup winners Lingard and Morrison were reunited on the pitch on Sunday.
Heaton was also back for United after re-signing from Aston Villa.
Chong struck first, latching onto a loose pass before clipping the ball into the Derby net.
After halftime, Pellistri finished coolly after a clever pass from Shoretire.
Derby pulled a goal back via Kazim-Richards and pushed for an equaliser, but couldn't find a way through.
Significantly, at the final whistle Rooney made a beeline for Teden Mengi, who is wanted back at Derby on-loan.
Solskjaer left Pride Park full of smiles and satisfied with a positive opening preseason win.
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