Sir Alex Ferguson warned the Barclays 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.

The equally inspirational Cristiano Ronaldo had already forced £9million goalkeeper Craig Gordon to beat away two free-kicks when he left the Scot for dead in first-half injury-time with a third.

The Portugal international, as well as defender Nemanja Vidic, had long departed for well-earned rests when Saha doubled his tally on the day with an 86th-minute penalty.

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."