Luis Suárez denied penalty, booked for protesting
The Barcelona striker was taken down by Rüdiger as he ran into the box; he reacted furiously. Messi ended up scoring from the move.
Update:

Luis Suárez was booked for vociferously protesting after being denied a penalty in this evening's Chelsea - Barcelona match at Stamford Bridge in the Champions League.
Our resident referee Iturralde González said of the incident: "It's a penalty, Rüdiger comes in from behind and ends up tripping him."

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Barcelona scored from the passage of play
Although Suárez was denied the penalty, the passage of play ended up with Barcelona scoring, after Chelsea won the ball back only for Christiansen to give it away to Iniesta, who passed to Messi for the Argentinean to score.

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Turkish referee Cüneyt Cakir let the play go on and then booked Suárez after the goal for his dissent. It's the first yellow card the Uruguayan has picked up in this edition of the Champions League.