With almost five minutes of injury time played, it looked as though Liverpool would take a deserved lead to Stamford Bridge for next week's second leg.
However with Austrian referee Konrad Plautz looking at his watch, Chelsea substitute Salomon Kalou lofted one last high ball into the Liverpool penalty area.
Riise (right), who had replaced the injured Fabio Aurelio after 62 minutes, stooped to try and head the ball clear, but instead headed it past helpless goalkeeper Pepe Reina and into the roof of his own net.
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