Their next league fixture is at Chelsea where they will have the opportunity to put a six-point gap between themselves and the Blues.
"Sunday is a massive game," said Ferguson. "That will go a long way to establishing what happens at the top of the league.
"We are 16 games undefeated. Now we have to make it 17."
Wenger, meanwhile, was unhappy with the playing surface in Manchester but he praised the opposition backline for frustrating Arsenal's attack.
"If I ask you do you want a good pitch or a bad one, what do you say?" he added.
"They made technical mistakes as well because the pitch is not good enough to play good football. It is bouncy and slippery.
"Overall, you have to give credit to United's defensive quality.
"We tried everything to create chances. I thought we were unlucky to lose the game, but we have to take encouragement from tonight's performance."
Phelan delighted with three points against Arsenal
Wenger, whose team have not beaten title challengers United or Chelsea in 11 encounters said he was not worried by his side's form against their rivals.
"Calm down," he insisted.
"You have to be realistic and objective and not necessarily reach big conclusions. I am here to analyse one game.
"It is a big frustration and disappointment but I don't know how big a blow it is to our title chances," he stated.
"What is important is that we bounce back in our next game [at home to Stoke on Saturday].
"Overall, on what I have seen there is no reason not to believe.
"We know we can play better offensively and actually, we looked quite solid."
Park scored what proved to be the winner in the first half, with a header from Nani's deflected cross.
United could have enjoyed a more comfortable victory had Wayne Rooney not fired his penalty high and wide of the Arsenal goal, after the Gunners full-back Gael Clichy was deemed to have illegally handled.
Park's record against Arsenal is very good - he is in fantastic form
United manager Sir Alex Ferguson
Ferguson was left bemused by his striker's effort.
"It was an unusual penalty, normally Wayne always keeps them down, I've never known him to hit one over," he added.
Ferguson also paid tribute to Park, who scored for the fourth time against the Gunners.
"Park's record against Arsenal is very good, he is in fantastic form.
"Unfortunately we're going to lose him to the Asia Cup for seven matches, which is disappointing."
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