The Manchester United left-back Patrice Evra has signed a contract extension that will keep him at Old Trafford until 2014.

The 29-year-old has won three Premier League titles, a European Cup, and three League Cups with United – the last of which he lifted after captaining the team against Aston Villa last year.

"Ever since I arrived at United [in 2006], it's been a dream come true playing here," he said. "The fans, the players, the manager and the staff all work hard to make this club the best in the world.

"I have won a lot in the last five years, but I want to win more and I know that's the mentality of everyone here."

Wenger refused to answer when he was asked to explain why Arsenal found it so difficult to win against their main title rivals. Instead he blamed his team's lack of penetration against United on a "very bad" pitch.

When the subject returned to Arsenal's results in the big matches the Frenchman was visibly annoyed. "Why do we always seem to lose these big games? If you are a football specialist I leave this analysis to you," he replied, his voice laced with sarcasm. "Why do you ask me when you know everything? I believe we are here to analyse one game – the game of tonight. I know your job is to get to conclusions but I leave that to you.

"I've spoken about the game tonight. You have to be calm and be realistic and objective. United won the game tonight and you don't necessarily have to go to big conclusions. Be calm."

Wenger was aggrieved that "the technical quality of the game was very average on both sides". The match, he said, had been a "big disappointment and a big frustration" but he argued there were mitigating circumstances, namely the "bouncy and slippery" playing surface.

"The pitch was so poor in my opinion and the game suffered a lot from it," he said. "I ask you, 'Do you want a good pitch or a bad pitch?' What do you say?"

Park Ji-sung's winning goal, four minutes before half-time, moved United two points clear at the top of the table, with a game in hand. It also established a club record, with Sir Alex Ferguson's side now having gone 16 games unbeaten since the start of the season, beating the previous best, 15, which was set by Ron Atkinson's team in 1985-86.

"I hope we can make it 17," Ferguson said, looking forward to Sunday's game at Chelsea. "That's a very important game now and we are starting to get there in terms of our form. It's improving and, if the back four continue to play like that, it will give us a great chance.