The Premiership side need just two points from their final three games, in order to go through to the UEFA Champions League knockout stages.
Wayne Rooney was captain for the home side, in the absence of defender Gary Neville.
Paul Scholes opened the scoring after 39 minutes, with a great shot from 20 yards. John O’Shea made it two, in the first minute of the second half.
Richardson, who came on as a sub made it 3-0, after FC Copenhagen goalkeeper Christiansen misjudged a shot from the England midfielder.
Van der Sar – O’Shea, Ferdinand, Vidic, Evra – Ronaldo, Carrick, Scholes, Giggs – Rooney, Saha. Subs: Kuszczak, Brown, Smith, Solskjaer, Richardson, Fletcher, Jones.
Christiansen – Jacobsen, Hangeland, Gravgaard, Wendt – Silberbauser, Linderoth, Norregaard, Hutchinson – Allback, Berglund. Subs: Gall, Thomassen, Pimpong, Kvist, Brandrup, Hansen, Bergvold.