United were under pressure for long spells of the second half at Anfield and were clinging on for a point after Paul Scholes was sent off with eight minutes remaining for aiming a punch at Xabi Alonso.

But John O'Shea fired home from close range in the 90th minute after Liverpool goalkeeper Jose Reina spilled Cristiano Ronaldo's free-kick.

United, who won at Fulham last week thanks to a late Ronaldo goal, are now 12 points ahead of second-placed Chelsea and Ferguson has no doubts that his team are getting the rub of the green at the right time.

"Without question this is a massive result for us," Ferguson said. "We were very lucky today. Liverpool upset our rhythm a bit and we had a lot of narrow escapes.

"But that happens in championships. Last week at Fulham was a great example of that when we broke away and scored in the last couple of minutes. Today we've broken away and scored in the last minute or so.

"You need that bit of luck to win a championship, there is no question about it and we've got that in the last couple of weeks."

Although Chelsea can cut the gap back to nine points with a win at Portsmouth in Saturday's late match, Ferguson believes his team are equipped to hold off the reigning champions.

"I don't think anything is impossible in modern-day football," he said. "We experienced that in 1998 with a great lead. But we had horrendous injuries then and we have a stronger squad now."

That squad strength will be tested as Scholes will now serve a three-match ban and England striker Wayne Rooney could be sidelined with a knee injury suffered at Anfield.

With Ole Gunnar Solskjaer injured and Henrik Larsson's loan spell expiring soon, United will be short of attacking options.

Ferguson added: "Wayne has a got a knee injury. We will just have to see how it is tomorrow.

"Paul Scholes will miss the next three matches as well. I will have to see the incident again. I'm not sure what happened."