The former England international made his first appearance since arriving as a free agent following his departure from Manchester United in the close-season, playing 45 minutes for his new side in Gera.
Ferdinand started in the centre of defence alongside Richard Dunne but was replaced as one of several half-time changes with the score at 0-0.
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After a tight opening, QPR threatened an early goal in the eighth minute, Charlie Austin close to getting on the end of Danny Simpson's cross only for a defender to touch the ball away at the last moment.
Rani Khedira blasted an effort way off target on the half-hour mark, shortly before the heavens opened to send fans in the open stands running for cover.
Four minutes before the break, Leipzig went close to scoring as Khedira crashed a 25-yard free kick off the crossbar before, in the second period, John-Patrick Strauss shot into the side netting with just Robert Green to beat.
Leipzig continued to press, Denis Thomalla firing narrowly over the crossbar from the edge of the box on the hour and, two minutes later, the German team were ahead, Poulsen running away from Dunne and slotting beyond Green with a cool finish.
That lead was doubled 17 minutes from time, Poulsen lashing the ball into the top corner from just inside the area after receiving a pass from Strauss.
QPR failed to create any chances of note to force their way back into the game in the closing stages and Redknapp will be hoping for an improved display in their next friendly against Leyton Orient on Tuesday.