United cruised to a 4-0 victory at the Stadium of Light to leave Keane in little doubt as to the gulf in class between the teams at opposite ends of the Barclays Premier League.United's victory was every bit as comfortable as the scoreline suggests as they cut through the Black Cats at will to expose goalkeeper Craig Gordon at regular intervals.
Goals from Wayne Rooney, Louis Saha and Cristiano Ronaldo before the break left the result in no doubt, and Ferguson was even able to withdraw the hugely impressive Portugal international with more than half an hour remaining.
• Fergie expects Rooney rush
Saha rubbed salt into the wound with an 86th-minute penalty after Nani had been tripped by Danny Collins.United headed back across the Pennines having reached the mid point of the season firmly in the title race, while the man who for more than 12 years led their charge for glory on the pitch has just 14 points in the bag and a long haul towards safety.
Keane knows the bulk of his side's points this season will not be taken from the likes of United, Arsenal, Chelsea and Liverpool, but from the sides in the battle for top-flight survival.
However, having seen them compete creditably in narrow defeats at both Old Trafford and the Emirates Stadium already, that was the very least he expected at the Stadium of Light today.
What he got in the opening 45 minutes was graft and commitment, but what his players lack was abundantly clear as United, despite barely getting out of second gear, took them apart so comprehensively that damage limitation was the only thing on the minds of the bulk of a Boxing Day crowd of 47,360.
Despite leaving Ryan Giggs and Anderson at home and Carlos Tevez and Patrice Evra on the bench, Ferguson was able to field a side which had simply too much class, pace and guile for Keane's team, which included for the first time 17-year-old striker Martyn Waghorn.
Where Tomasz Kuszczak had only one save to make in the first-half when he tipped over Ross Wallace's 40th-minute drive, opposite number Craig Gordon was peppered throughout.
Had he not pulled off fine saves from two Ronaldo free-kicks and a Wes Brown header, United could have been six goals to the good by half-time.
As it was, they were 3-0 up courtesy of some scintillating passing and movement, as well as top-class finishing.
Rooney set the ball rolling on 20 minutes when, after full-back Brown had played a one-two with Ronaldo, he slid the striker in to fire nonchalantly past Gordon.
Rooney turned provider 10 minutes later, accepting Ronaldo's pass from the United half before cutting inside Wallace to pick out Saha at the near post.
But it was the Portugal international who set the seal on a blistering start when he smashed home an injury-time free-kick with Gordon rooted to the spot.
Keane's response was to replace Wallace with the more combative Grant Leadbitter and withdraw Waghorn into a five-man midfield for the second half, although the Black Cats were pinned back inside their own half as United threatened to cut loose.
The was a brief glimmer of hope for the home side when Michael Chopra's enterprising run set up Dickson Etuhu to shoot on 51 minutes, but he skied his effort harmlessly over.
Former United defender Paul McShane denied Rooney a second with a 54th-minute block, but Kuszczak had to dive low to his right to keep out Kenwyne Jones' 56th-minute striker.
Ronaldo departed to warm applause from both sets of supporters a minute later with his job done as Park Ji-Sung was handed his first taste of first-team action since undergoing knee surgery in March.
The home side rallied as the clock ran down, but with the visitors in cruise control, genuine openings were few and far between.
Chopra saw a 75th-minute shot beaten away by Kuszczak, but it came either side of another Gordon save from Rooney and an uncharacteristically wild close-range volley from the United man.
There was, however more to come, and when Nani went down under Collins' challenge, referee Uriah Rennie pointed to the spot and Saha obliged.
Fergie expects Rooney rush
Sir Alex Ferguson warned the Premier League to beware a goal rush
from Wayne Rooney after watching him help put Roy Keane's Sunderland to the
sword.
The 22-year-old England international set United on the way to a resounding
4-0 victory at the Stadium of Light with a 20th-minute opener, his first league
goal since October.
Rooney then provided the cross for Louis Saha's second with half an hour gone
to leave Ferguson delighted.
He said: 'I have said before that strikers do go on little runs like that.
'It is his first goal for six games, but his goals have come in waves.
'When he got his injury (in the opening game against Reading), he was out for
a month and since then, he has been gradually getting towards what we have seen
of him today.'
Rooney's contribution to a victory which was every bit as comfortable as the
scoreline suggests was only part of the story as Keane's worst fears became
painful reality.
Ferguson said: 'It was an excellent performance, I thought the passing and
movement was excellent.
'The first goal put us in the driving seat because we knew Sunderland were
going through a bit of a sticky patch.
'It was a marvellous move for the first goal and after that, we did play
well.'
Keane, who won seven league titles and four FA Cups during his glittering
spell at Old Trafford, was philosophical after a defeat which left his side
sitting in 19th place in the table with just 14 points at the season's
mid-point.
He freely acknowledges they have a major fight on their hands, something he
did not expect, but remains convinced they can get themselves out of trouble.
Keane said: 'We would have liked a few more points on the board - I certainly
feel we deserve a few more points - but we haven't, that's the reality of the
Premier League.
'We are where we are. The best team will win the league and the three worst
teams will go down, and I believe we are not one of the three worst teams in the
Premier League.
'But it would be nice to back that up with some positive results and some
wins.
'It is never nice to lose any game, particularly at home, but if you are
going to be beaten 4-0, then why not by a very, very good team?'
Keane, armed with a transfer kitty of around £20million, will attempt to
strengthen his squad during next month's transfer window, and hopes the Black
Cats' pulling power remains intact despite their lowly league position.
He said: 'Obviously, if we were higher up in the table, it might be different
attraction.
'But I always hope, and I believe, that Sunderland will be an attraction for
players anyway.
'We had 40,000-odd here today again, and we hope Sunderland will always be an
attraction for any player.
'That's what I will be saying if I get a chance to speak to one or two
players.
'But let's not kid ourselves we are going to be bringing in loads of players.
We hope a few, two or three, but that might be about it.'
Sunderland 0 - 4 Manchester United
