Manchester United midfielder Juan Mata has admitted that the team's start to their Premier League defeat at Arsenal was "unacceptable".

The Red Devils lost 3-0 at the Emirates Stadium on Sunday, with all three Arsenal goals coming in the opening 20 minutes of the game.

Mata has vowed that Louis van Gaal's side will not repeat that kind of performance again.

"It's not easy to write today and to find words of encouragement after a game like this, but we have to carry on," Mata wrote in his blog on United's official website.

"As you could see, everything went wrong in the first half. Before the game, our goal was to keep the top spot of the Premier League, but it wasn't our day as we saw from the kick off.

"Arsenal started with more intensity, they scored very quickly and with no time for our reaction they scored the second goal. Not even 10 minutes have passed and things were already looking very bad. A start like this from us is unacceptable; if we want to fight for big things we must learn the lesson as soon as possible."

Arsenal have moved ahead of United into second place in the table following the result.