It was when Sir Alex Ferguson was reminded that his Manchester United side had held a 15-point lead over Chelsea barely two months ago that his face hardened a little and, briefly, there was the sense he had taken it as a personal affront.

"I don't know how many points we were in front of Chelsea at any given time," he replied, and it was here that his voice picked up speed and he made sure to keep eye contact. "It doesn't matter. Where we are today is exactly where we are. It doesn't matter what happened last Sunday, four Sundays ago, four months ago, four years ago, we are where we are. We have three games left, we're three points ahead, same goal difference, playing at home, two home games and one away. That's where we are. Nothing can change it."

He was sitting in the same room at United's training ground where, in one of those epic tussles with José Mourinho a few years ago, Ferguson interrupted one press conference to point at the blue skies over Carrington. "The birds are whistling here and the sparrows are waking up at Stamford Bridge coughing." It was here, too, around the same time, that Ferguson's mobile phone went off in another conference. United had just moved to the top of the league. "It's José," he said, scrabbling around in his top pocket and grinning mischievously. "He's panicking already."

On this occasion, the mood was not so light. United have never surrendered a 15-point lead to lose the title and they will be acutely aware that Chelsea won this corresponding fixture 2-1 in April last year. Another win at Old Trafford on Sunday will mean Carlo Ancelotti's team move to the top of the league for the first time since December, with two games to go.

Ferguson, maybe not coincidentally, spoke for the first time about the importance of United overtaking Liverpool by winning a record 19th league title. "It's not important for me, but it is for the history of the club." The alternative, by his own admission, would be unbearable, comparable to any of the disappointments he has encountered in almost a quarter of a century in charge.

Ferguson, nonetheless, was emphatic when he was asked whether United should still be considered as the favourites. Away from home, it has been a strangely unproductive time for United with only five wins, meaning they could be the first team since Liverpool in 1976-77 to win the league with fewer than eight victories on the road. "Our record has been – how would you put it? – ordinary," Ferguson conceded. At Old Trafford, however, it has been a remarkable story of success, the 2-2 draw against West Bromwich Albion in October being the one occasion when they have dropped points. "We've had a lot of criticism about our away form and rightly so because I've not been happy myself sometimes because I've not been happy myself sometimes," Ferguson said. "But the realisation of that has made us really step up to the mark at home. The home form has been fantastic, probably the best in Europe."

It certainly feels like a long time now – 398 days, to be exact – since Joe Cole and Didier Drogba scored past Edwin van der Sar to condemn United to their last home defeat. In all competitions, United have played 30 home games since. They have won 27 and drawn three, scored 68 and conceded 15. Most remarkable of all, Cole's effort 13 months ago was the last time an opposing player has scored a first-half goal at Old Trafford in the league.

Ferguson spoke about the improvements to the Old Trafford pitch, which has not been relaid since 2003, when it was once the bane of his life. "By December, January, February, the bad winter months, that was when the pitch used to break up. It's no longer that way now. It's absolutely perfect, the best we've ever had."

Another conclusion would be that many of United's opponents appear to consider trips to Old Trafford as an exercise in damage limitation, just as was once the case at Liverpool during their period of domination. Blackburn Rovers sieved seven goals, Birmingham City five. Others, notably Sunderland and West Ham United, have meekly raised a white flag and that has left United on course to go through an entire league season unbeaten at home for only the eighth time in their history.

Ferguson (1999-2000 and 1995-96) and Sir Matt Busby (1955-56 and 1966-67) have both done it twice. There were two occasions in the Newton Heath era, in 1894-95 and 1896-97. Ron Atkinson also managed it in 1982-83, the last time United went unbeaten at Old Trafford in all competitions. There has never, however, been a home record in United's history as formidable as the current set of results.

"Everyone comes here knowing they are going to get a hard game," Ferguson said, and the manager's ethos could be summed up when it was pointed out that a draw would be a decent result. "We won't be going for a draw. Everyone knows that. Chelsea know that. Our fans know that. Everyone sitting in here knows that. There's no point discussing draws."

Nor did he want to consider the prospect of losing yet, for once, Ferguson was happy to expand on what it would mean to overtake Liverpool on 19 titles. "I certainly didn't think we could do that when I took over," he said. "The target was to win the title. I got it and, since then, the club has taken off."