Martyn Waghorn's 33rd-minute strike was enough to defeat United, who enjoyed much of the pressure in the second half without making their pressure pay.
McArthur admitted Wigan left plenty of room for improvement but after only one win in their last five games, the Man of the Match was delighted to claim the three points.
He said: "The result was the main thing. I don't think we played well at all, we were very scrappy which is unlike us. But it's another three points and we'll take it."
McArthur could not pinpoint the reason behind Wigan's below-par performance: "I'm not sure. We've obviously had a lot of games this year but I don't think that's an excuse.
"We're better than we showed today but we had to display a lot of resilience to win the game."
Wigan go to Wembley as FA Cup holders for a semi-final against Arsenal, but McArthur refused to acknowledge whether that was not a factor in their recent form.
Asked if Wigan can return to Wembley again in the Play-Off final, McCathur said: "We've got another game before the FA Cup semi-final, but when it comes around, we will give it out best shot."
Waghorn was delighted to celebrate becoming a permanent fixture in Uwe Rosler's squad by scoring the winner a day after completing his move to the DW Stadium.
"Obviously it's nice to get the winner in a big game.
"It was tight. Leeds worked hard and pressured us. It's a scrappy win but much-needed in the end.
"This a massive club, I want to get settled and start enjoying my football again."