London strategist Arsene Wenger pointed out poor condition of the "Old Trafford" stadium pitch as one of the reasons for the club's defeat.
In Monday's Premier League match, the 'Red Devils' defeated the visitors from the capital 1-0 and rose to the first place in the league table.
"The pace was huge, but the quality of the pitch was very poor," said the Frenchman. "It was difficult to play technically, so we saw a lot of mistakes from both teams."
Wenger also praised the opponents' defense: "I have to note that the 'Man Utd' defense played excellently. We did everything to create opportunities to score."
"I think we were unlucky that we lost, but we have to see this evening as encouragement."
'Man Utd' manager Sir Alex Ferguson echoed his colleague: "The defensive quartet played superbly. Our form is improving and the defense is finding consistency, which is crucial for achieving good results."
The Scot congratulated the Korean Ji Sung Park, who scored the only goal: "He always plays successfully against 'Arsenal' and is in great athletic form. It's a pity that we will be without him for seven matches due to the Asia Cup tournament."