Sir Alex Ferguson admitted Manchester United are under pressure to win their three remaining home games this season after their lead at the top of the Premier League was cut to five points following a surprise, but thoroughly deserved, defeat at Wigan Athletic.

United's eight-point advantage was trimmed by Shaun Maloney's fine goal for Wigan, who lifted themselves out of the bottom three for the first time since December with their first result against the Old Trafford club in 15 attempts since winning promotion to the Premier League in 2005. "This is the first time this club has ever taken a point from Manchester United. You can imagine what it means," said Roberto Martínez, who denied reports he is to quit as the Wigan manager at the end of the season.

Ferguson lamented the performance of the referee Phil Dowd and particularly the refusal to award a penalty to United when Maynor Figueroa handled Phil Jones's cross in the 72nd minute. The appeal was rejected by the assistant referee David Richardson, who controversially denied Wigan a first-half lead when he adjudged Gary Caldwell had fouled David de Gea as Victor Moses headed home. The United manager also claimed the corner that led to Maloney's winner should have been a goalkick. Even so, he admitted United had no excuse for such a lethargic display at a critical stage of the season.

"Figueroa didn't seem to handle it – he did handle it," the United manager said. "The thing is, if he had been close to Phil Jones then you would say you are not going to get that kind of decision but he was 15 yards away. That was disappointing. Sometimes you get the breaks and sometimes you don't. Last Sunday we got a break [against QPR] and it evens itself out over the season. They talk about the big clubs getting all the big decisions but tonight we didn't get one.

"I thought Phil Dowd had a disappointing night, I must say. That doesn't deflect from the fact that Wigan were the better team. We were second to every ball and only had one shot at goal. It was one of these off-nights you get. We have been on a great run. It has been tremendous and it has put us in a position where we can win the league, and we have to get over the disappointment of tonight."

United travel to City on 30 April and also face Sunderland away on the final day of the season, but Ferguson believes a maximum return at Old Trafford against Aston Villa, Everton and Swansea City will be required to secure the club's 20th league title. He said: "It was a disappointing performance throughout the game. We didn't reach a level we have been used to in the last few months. A couple of months ago City were something like 5-1 on and we were well behind them in terms of goal difference and points, and we have to take some credit that we have got ourselves back into the race. It is important to win our home games now."

Ferguson was keen to pay tribute to Wigan's outstanding display, which elevated them two points clear of the relegation zone. He said: "You have to recognise that Wigan are in a false position. They have played some of the best football in the league. Despite their position they have played their football all night and you have to give them credit for that. They are a very, very under-rated team. With them playing the three centre-backs it gives them a lot of time on the ball. We decided to go against them in the second half and that was better for us but in the first half we were completely dominated. It was one of these off nights. It is unavoidable sometimes."

Martínez described the victory as a historic night for Wigan and praised his players for refusing to dwell on Chelsea's two controversial goals in the 2-1 defeat at Stamford Bridge on Saturday. "It would have been very easy to blame someone else but we showed a very mature approach," the Wigan manager said.

"I loved the arrogance of the players tonight. We defended very well but we were patient on the ball and played Manchester United eye-to-eye."

The Wigan chairman, Dave Whelan, also denied Martínez will leave the DW Stadium this summer, regardless of the team's fate. "I have always said that Roberto will leave one day for a big Premier League club, or one in Europe. But at the moment he is glued to Wigan, just like I am," said Whelan. "The spirit in our camp is high and I am delighted to be out of the bottom three. We firmly believe we can stay up. Roberto has been saying that all season. We are a good team and this proves it. If we stay up it is worth £40m – what a goal."