Seven-year-old United fan Jude Grayson, from Spennymoor in County Durham, joined captain Jamaal Lascelles in leading the team out for the game at St. James' Park, which Steve Bruce's side won 1-0 thanks to Matty Longstaff's goal.
Accountancy firm Anderson & Co sponsored the match, but director Paul Anderson generously donated the package to the Angel Trust, a charity based in Bishop Auckland, and invited applicants for the mascot place.
Jude, who was diagnosed with leukaemia in April and faces three years of treatment, was nominated by several members of the public and chosen by Mr. Anderson to receive the prize but, two weeks before the game, suffered a reaction to his treatment which caused a cardiac arrest and led to him being placed in intensive care.
Dummett heard about Jude's story and, when the youngster was able to come out of an isolated ward, arranged independently to visit him at Newcastle RVI earlier this month, spending more than an hour talking to the youngster and his family as well as giving him a signed pair of his football boots.
"He was absolutely fantastic and only left after an hour because Jude had to go for some tests," said the youngster's mother, Kerry. "It really lifted his spirits.
"And despite everything he's been through, Jude was absolutely determined that he was going to walk onto the pitch on Sunday. Jamaal Lascelles offered more than once to lift him up but there was no way Jude wasn't going to run on the pitch and kick a ball at St. James' Park.
"Everyone was brilliant from start to finish. I can't thank Paul Dummett and the club enough, and Paul Anderson for giving him the opportunity to be mascot."
Hospital staff discharged Jude on Friday night, meaning he could go to St. James' Park on Sunday. Dummett was a substitute for the match against the Red Devils, so was unable to walk out with Jude, but he spent more time with the family after the final whistle and gave Jude his shirt from the game.
"When I saw him on the pitch, it touched your heart when you see how determined he was to go on the pitch and kick the ball at St. James' Park," said Dummett. "Even after the game, it took it out of him being there all day because he was going through so much, but he'd had a great day.
"I've got a niece and nephew, and Jude's got a brother and sister, and it just shows you need to appreciate everything you have when you see how hard it is for Jude and his family.
"But since I saw him in hospital, he's improved so much; even walking onto the pitch at St. James' Park, because when I saw him in hospital he was struggling to walk. He had to hold onto things just to walk to the toilet, so he's made rapid progress.
"I've kept in touch with his mam and dad, who say he's improved so much, so hopefully he can keep on improving and the treatment works so he can better soon.
"I've formed a real bond with him and I - and everyone at the club - wish him all the best."
