Man Utd: Van der Sar, O'Shea, Ferdinand, Vidic, Evra (Simpson 67), Ronaldo, Carrick, Anderson (Fletcher 72),Giggs (Nani 72), Rooney, Tevez.
Subs Not Used: Kuszczak, Park.
Newcastle: Given, Carr, Taylor, Cacapa, Jose Enrique, Milner (Viduka 64), Smith, Butt, N'Zogbia, Duff,Owen (Rozehnal 82).
Subs Not Used: Harper, Emre, LuaLua.
Att: 75,965
Where do we go from here? God only knows, but we need to get ths sorted out as soon as possible.
Some say defeat to Stoke on Wednesday and the season is over. But on this showing it will go to the wire, because we could be facing a relegation battle!
Hat-trick hero Cristiano Ronaldo led a merciless second-half destruction of crisis-club Newcastle as the Red Devils soared back to the top of the table.
While the managerless Magpies stagger from one setback to another, the Red Devils seem intent on adding a 10th Premier League title to their regained status as the world's richest club.
And with Ronaldo in this mood, it is difficult to see how they can be stopped.
After a goalless opening period, the Portugal winger broke Newcastle's resistance with a low free-kick, added a startling second with a neat finish to a move involving Wayne Rooney and double scorer Carlos Tevez, then completed his first Red Devils three-timer two minutes from time.
Ronaldo now has 22 goals for the season, which puts him on a par with another legendary marksman, Alan Shearer, the man whose name Newcastle's long-suffering fans are demanding should succeed Sam Allardyce following Harry Redknapp's high-profile snub.
If the backdrop to Newcastle's trip from Tyneside was bleak, the return journey would have been positively thunderous as owner Mike Ashley and chairman Chris Mort ponder their next move.
Without a boss since Allardyce's departure on Wednesday and rejected by Redknapp at lunchtime, stand-in boss Nigel Pearson described morale as no better than 'OK' immediately before kick-off.
As the Geordies last tasted victory at Old Trafford in 1972, three years after they last won any trophy of note, it was hard to escape the feeling they would be little more than lambs to the slaughter.
After all, Arsenal's surprise draw with Birmingham had provided Sir Alex Ferguson's men with the extra incentive of knowing an 11th straight win on home soil would send them back to the top.
And, following a hard-fought opening period, the theory proved fully justified as the hosts cut loose in amazing style. Quite aside from Ronaldo's heroics, Tevez scored twice and Rio Ferdinand blasted home an impressive volley from Rooney's chipped pass.
The game ended with Newcastle skipper Alan Smith dismissed for his protests at Tevez's rout-completing effort, which may, or may not have crossed the line.
It seemed a spurious point for Smith to question given the state of the game. And, when he finds out what happened, Allardyce and Redknapp, in their different ways, are probably both relieved to be well out of it.