Ferguson saw Didier Drogba latch onto the Liverpool midfielder's back pass to fire Chelsea in front at Anfield as they briefly extended their advantage to four points.
United's 1-0 win on Wearside reduced the gap again to a single point, but the Blues remain in the driving seat for next weekend's dramatic finale.
Ferguson said: "I just saw it after the game. It was a great gift. There's nothing we can do about it now, we just have to get on with it."
If Chelsea beat Wigan at home next Sunday - they lost 3-1 at the JJB Stadium in September - the trophy will be heading for Stamford Bridge regardless of what happens at Old Trafford, where Stoke are the visitors.
But Ferguson knows from experience that nothing is ever certain in football.
He said: "All we can do is win our game next week. We want to do that, we are playing in front of our fans in the last game of the season.
"I won't insult Wigan in any shadow or form because I think they are a really good football team.
"They will have a go and you never know what happens in football. It's a crazy game."
United's neighbours could do them a massive favour next weekend, although Ferguson admits that might a tough task.
He said: "Manchester City did us a great turn by beating them [Chelsea] twice, and they (Wigan) are another neighbour.
"Listen, we are clutching at straws a little bit, but the important thing is for us to win our game and enjoy it in front of our fans.
"There will be 76,000 there, we will play the right way and we will play with a lot of dignity in our game. You never know."
Nani's 28th-minute goal was enough to claim all three points on an afternoon when United could have won much more comfortably.
Dimitar Berbatov missed a trio of glorious chances although Sunderland had their own opportunities before the break when John Mensah and Lorik Cana both headed wide and Steed Malbranque saw a well-struck drive turned over by Edwin van der Sar.
However, Craig Gordon was by far the busier of the two goalkeepers and Michael Turner had to hack a 78th-minute shot from substitute Michael Carrick off the line.
Ferguson added: "We were just careless in our finishing, I suppose. It looked that way. We had great chances.
"They probably felt they were comfortable but we got there, that's the important thing, three points.
"A 1-0 victory away from home is always a good result."
Former United defender Steve Bruce, who admitted his side had lacked quality in the final third, said: "It takes it to the last game of the season but it would take an almighty collapse by Chelsea and, if we are being honest, I don't think you can see that at the moment.
"You can't see Wigan going and getting a result, but you can never say never, can you? But they (United) are not going to give it up, that's for certain, he'll not give it up."
Bruce was more concerned with the suspected cruciate ligament injury suffered by young midfielder David Meyler, who was due to link up with the Republic of Ireland for a training camp later his month, just a week after he signed a new five-year contract.
He said: "We are fearing he has done his cruciate knee ligament so that's a huge blow because the kid has had such an impact for us.
"We hope that it's not too bad. He's going to have scans and X-rays over the next 24, 48 hours."