The European champions overcame the sending off of Nemanja Vidic, who was shown a red card four minutes into the second half in Yokohama for elbowing LDU striker Claudio Bieler in the face.
“We’re the best team in the world,” said Rooney, who was named player of the tournament after scoring twice in United’s 5-3 semi-final win over Japan’s Gamba Osaka.
“If we hadn’t won it would have been difficult going back home. We would probably have been on a downer and it would have had a knock-on effect.
“Now we can go back with lots of confidence. It’s been a childhood dream. I just looked at my phone and I had a message saying ‘Congratulations—you’re a world champion’.
“To score the winning goal is a great feeling.”