Goalkeeper Harrison told manutd.com: "The emotions were really high in the game and also in the changing room just then.
"Everyone was celebrating so much in there and I couldn't even get my suit on as it was soaking wet! Everyone was enjoying themselves and I am glad we won.
"It was a great feeling to have some big saves in the game to keep us in it. I am happy with myself."
Captain McAllister also said: "I am absolutely buzzing and I am proud of all of the lads, even the lads that haven't participated tonight.
"We have done this over the course of the season, together. Some people have played more minutes than others but ever since that first game against Reading we have all put in a shift.
"We have been the better team each time and when we have suffered, we have suffered together. We deserve this more than any other team in the country."