"This shows who the best team is - all game we dominated," Rooney told BBC Radio 5 Live after United's 3-2 win. "The young lads made the difference - Danny Welbeck, Tom Cleverley, Phil Jones, Chris Smalling - they were all outstanding," he said. "I think this was a footballing lesson," he added later on Twitter. United were 2-0 down at half-time at Wembley but recovered when 21-year-old Chris Smalling pulled a goal back before Nani struck twice to complete an unlikely turnaround.
Despite doing it the hard way, Rooney believes they outplayed their rivals. "They had five minutes where they scored two goals, and that was about it." Rooney said. "The score-line is deserved because of our passing, and the brilliant chances we created. We are champions and we are the team to beat - we need to go out and prove that.
"Full credit to the whole team, that's our attitude. We never know when a game is finished. We hope title number 20 will come. But it's a long season and there's a lot of good teams in the league. Our main aim is to win that title again."Welbeck and Smalling both started for United with Cleverley, Jones and Rafael Da Silva introduced as substitutes, bringing the average age of United's team down to 22.
Cleverley, who provided the assist for United's sumptuous second goal, was glad he was one of the young players to whom Ferguson handed an opportunity. "It was a big game for us, and to show we can win with a young team in the second half is very good for the club. This is good experience for me to try and stake a claim this year," Cleverley told BBC Radio 5 Live. "To come back from 2-0 down in any game is good, but it's even sweeter in a Manchester derby," he added.
United boss Sir Alex Ferguson reserved special praise for Nani, who he believes is finally fulfilling his potential. "Nani had a fantastic season (last season), he was just unfortunate that Antonio Valencia came back at a time when we needed a boost and some freshness," Ferguson said.
"Valencia has been terrific but Nani has been great in pre-season and he will start the season. He has always had great potential. Some players take longer than others to mature."
When asked whether new United goalkeeper David De Gea should have kept Edin Dzeko's strike out, Ferguson was not critical of his new number one. "Well it was bending a little bit... it's difficult to say," he said. But De Gea, 20, admitted that he must continue to work hard at his game. "Football is football here and in any country. I have to adapt quickly and improve on the whole of my game."