Manchester City manager Roberto Mancini admitted bitter rivals United deserved to edge the Community Shield with their 90th minute Nani winner.
City went into the half-time break at Wembley 2-0 up, thanks to goals from Joleon Lescott and Edin Dzeko.
Chris Smalling reduced the arrears before Nani's brace sealed the win.
"Maybe they played better than us," said Mancini. "But the right result after 90 minutes would probably have been 2-2."
City enjoyed a dream start when, after weathering some early pressure, they took the lead.
Lescott headed home David Silva's fantastic centre before Dzeko's 35-yard shot beat United's debutant keeper David De Gea.
United showed plenty of fighting spirit after the break and were soon level thanks to Smalling and Nani, with a wonderful finish.
The Portuguese winger then sealed United's 19th Community Shield victory when he capitalised on Vincent Kompany's mistake to round Joe Hart and slot the ball home.
"I am disappointed with the result," said Mancini. "It was the first game of the season, and anything can happen because all of the team are not in good form.
"We are disappointed but it is important we understand why we made the mistakes."
Mancini also denied City had made any approach for Inter Milan midfielder Wesley Sneijder. Manchester United have been linked with the Dutch playmaker for most of the
summer but reports over the weekend claimed City were now in for the player.
But Mancini said: "No," he said. "It is not true.
"He is an Inter Milan player. We never spoke about him."
Meanwhile, City skipper Kompany does not believe the result will have any bearing on his side's Premier League title challenge.
"It would have been nice to win it, obviously, but the fact that we didn't win it is not going to change anything about how we work towards the Swansea game (next Monday)," he told talkSPORT.
"If anything it's good that we have another 90 minutes in our legs. It wasn't our best performance today but next week is going to be the big one.
"We've got a lot of potential so come the league, come the Champions League, come the FA Cup we'll be ready for it, there's no doubt about it."