The Leeds head coach delivered a tactical master-class as Leeds stifled the Reds on home turf, barely allowing them a sniff of goal.
And at the other end a 24th-minute header from Kemar Roofe and a crisp finish three minutes from time from Ezgjan Alioski earned the visitors a deserved three points.
Felix Wiedwald barely had a save to make in the Leeds goal as Mark Warburton’s side saw their positive start to the campaign brought to a juddering halt, Leeds finishing the day in third place in the Championship table.
“This could probably be our best game so far,” said Christiansen. “Tactically we neutralised a very good Nottingham Forest side who had just beaten Middlesbrough and Newcastle.
“We have beaten them on their home ground and not only am I happy, I am also very proud of my players. Everyone was very good today. When you get the second goal you know that the game can be closed out, in that moment.
“This league is amazing, however, and even with five minutes left, you know that you can still concede goals.
“But it is great that we have kept four clean sheets now. It looks good on the table, but it is also good for the confidence of your defenders and your goalkeeper.
“It is the work of the strikers, the wingers and the midfielders that gets you these results as well and today everyone gave 100 per cent.”