Michael Owen and Ryan Giggs shone as Sir Alex Ferguson's much-changed side taught their old rivals a lesson in finishing.
Owen set United on their way after 15 minutes with a neat finish before he doubled his tally with a stunning strike from the edge of the box.
Giggs added a third before the break when he fired into the net from a tight angle.
More to follow.
Let's get the party started: Michael Owen slots the ball home to put Manchester United in front
MATCH FACTSLeeds: Lonergan, Lees, Bromby, O'Dea, White, Snodgrass, Clayton, Howson, McCormack (Nunez 66), Becchio (Forssell 52), Keogh (Vayrynen 52).
Subs not used: Rachubka, O'Brien, Brown, Taylor.
Man Utd: Amos, Valencia, Carrick, Fryers, Fabio Da Silva, Park, Diouf (Welbeck 70), Giggs (Pogba 46), Owen, Berbatov, Macheda (Cole 77).
Subs not used: De Gea, Brown, Keane, Thorpe.
Referee: Mike Jones.
Off and running: Owen (centre) celebrates after scoring the opening goal against Leeds
You beauty! Owen fires in his second goal to double United's advantage against Leeds
Duel: Owen (left) challenges Leeds United's Jonathan Howson during the Carling Cup third round tie
Hands off! Luciano Becchio of Leeds is tackled by Ji-Sung Park of Manchester United (left)
Ryan Giggs (second left) celebrates scoring United's third goal just befoere half time at Elland Road
Crunch: Leeds' Aidan White is tackled by Mame Diouf during United's win at Elland Road
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