Sir Alex Ferguson has hailed Sunderland's recent win at Chelsea as "the perfect performance".
Ferguson sends table-topping Manchester United into battle against the Black Cats at Old Trafford on Boxing Day already acutely aware of the challenge posed by Steve Bruce's men.
A goalless draw with United at the Stadium of Light earlier this season forms part of a succession of positive results against the Premier League's big guns by Sunderland this season.
Victory was achieved against Manchester City and draws collected against Arsenal, Liverpool and Tottenham, in addition to that stalemate with United, which Ferguson regards as the most difficult away game his side have faced all season.
But eclipsing all those was the three-goal triumph at Stamford Bridge five weeks ago.
"In all the time I have been at Manchester United, I could probably point to six perfect performances," said Ferguson.
"Steve will look at that in the same way. It was one of the stand-out performances of the season.
"They were absolutely brilliant and could have won by six or seven.
"It is a reminder that we are dealing with a team that has that kind of ability and drive at the moment. We are in for a particularly hard game."
It did not escape Ferguson's attention that one of his own helped do the damage that day.
Having loaned Danny Welbeck to Sunderland for the campaign, Ferguson has been encouraged at how the 20-year-old has eased himself into the first-team picture.
Taking advantage of the knee injury that has ruled one-time Old Trafford colleague Frazier Campbell out for six months, Welbeck has responded positively to the challenge provided by fellow
forwards Darren Bent and Asamoah Gyan.
He has scored four times since breaking his drought at Stamford Bridge and, although he cannot face his parent club on Sunday, Ferguson confirmed he believes Welbeck is now one of Sunderland's main men.
"In his spell around the first team in the last couple of years, Danny never played more than four games in a row," observed the Scot.
"It was imperative that he went out on loan and played regular football."
In addition, part of the aim was to get Welbeck used to his own body, which had been growing at an alarming rate.
"In the last couple of years he grew so big, so quickly, Danny was weak in some parts of his legs, which created a lot of problems for the boy.
"But you look at him now and see the growth. He has filled out and is very powerful.
"He is handling the physical part quite easily and has been one of Sunderland's best players."
All things considered, Ferguson is probably quite pleased Welbeck is consigned to the stands at Old Trafford.
In confirming the clock is ticking down on Edwin van der Sar's career, the United chief started to usher in a new goalkeeping era, offering a positive assessment of Anders Lindegaard's first few days at Old Trafford.
But van der Sar will be the man he relies upon on Sunday as United look to retain pole position in a league that is becoming more intriguing by the week.
"I am surprised that people are still surprised at how tough this league actually is," said Ferguson, who will be without Paul Scholes and John O'Shea due to groin and calf problems respectively. "Sunderland are a perfect example.
"A few weeks ago, they were down near the bottom of the league. Now they are challenging for a UEFA place. Win a few games and you can put yourself right back up there.
"It is so tight."
Ferguson is looking no further forward than the January 4 meeting with Stoke, after which Lindegaard will be available.
That clash with Tony Pulis's men brings the curtain down on a packed festive Premier League programme, when, weather permitting, Ferguson will be able to assess where the strongest title challenge to his own team should come from.
"My aim is to try and be top by January 4," he said.
"By that time, the top of the league will have taken shape.
"Maybe, because of the weather, it is difficult to think everyone will have four games. But if we do, and we are top, we will have done well."