Union Berlin struck twice late in the game to come from a goal down and beat hosts RB Leipzig 2-1 on Saturday, taking revenge for their midweek last-gasp German Cup semi-final exit at the hands of the same opponents.
Leipzig had beaten them on Wednesday by the same score thanks to Emil Forsberg's stoppage-time winner.
Poulsen scored a minute after the restart as the Europa League semi-finalists looked to tighten their hold on third spot.
Leipzig, who face Rangers in the Europa League last four on Thursday, were hardly a threat in the first half.
But Poulsen curled his low shot in a minute after the restart before Nordi Mukiele came close to a second in the 73rd when he hit the post from a tight angle.
Instead, Union left it late to strike twice, stunning the 45,000 crowd.