Manchester United recovered from their Champions League exit against AC Milan by easing into the FA Cup semi-finals.
Roy Keane put holders United on course for victory over Southampton after two minutes, and goals either side of the interval confirmed their supremacy.
Cristiano Ronaldo took advantage of good work by Wayne Rooney to score the second in first-half injury time.
Paul Scholes added a third from 12 yards in the 47th minute, then headed home four minutes from time.
United stamped their authority almost instantly, with Keane putting them ahead in the second minute.
Quinton Fortune's poor corner was only partially cleared and Keane was allowed to turn and fire home, via a crucial deflection off Peter Crouch.
Southampton were in danger of being swept aside, with Rooney having a shot turned on to the bar by goalkeeper Paul Smith before missing a simple header from the rebound.
Rooney was again denied by the woodwork two minutes before the interval, with Smith once again getting a crucial touch on to the post.
But as Saints somehow looked set to survive the first period only one goal behind, United deservedly doubled their lead.
Rooney was once again the instigator with a powerful run past two defenders. He found Ruud van Nistelrooy, who set up Ronaldo for a comprehensive finish.
And Southampton were left with no way back after 47 minutes when more good work by Rooney and Van Nistelrooy left Scholes with room to drive home from 12 yards.
The celebrations were marred when a United fan threw a red flare into the Southampton goal-mouth and held up the re-start.
Smith was the only man standing between United and a rout, and he saved brilliantly from Van Nistelrooy as he flashed a shot towards the top corner.
Southampton barely threatened United, and it was no surprise when Van Nistelrooy and Rooney combined again for the Dutchman to cross for Scholes to head in at the far post.
Southampton: Smith, Cranie, Lundekvam (Davenport 45), Jakobsson, Higginbotham, Telfer, Oakley, Anders Svensson, Bernard (McCann 62), Camara (Phillips 80), Crouch.
Subs Not Used: Niemi, Nilsson.
Man Utd: Howard, Brown, Ferdinand, Silvestre, Heinze (O'Shea 60), Ronaldo (Smith 68), Keane (Phil Neville 70), Scholes, Fortune, van Nistelrooy, Rooney.
Subs Not Used: Carroll, Bellion.
Goals: Keane 2, Ronaldo 45, Scholes 48, 87.
Ref: H Webb (S Yorkshire).