Imperious Barcelona thumped visitors Borussia Dortmund 4-0 in their Champions League quarter-final first leg on Wednesday after Robert Lewandowski netted twice against his old club to earn the Catalans a sizeable lead. The treble-chasing Barça predictably dominated the opening stages and grabbed the lead following Raphinha's strike in the 25th minute. A string of saves from Dortmund keeper Gregor Kobel frustrated Barça for the remainder of the first half. Barcelona emerged more determined following the break and it took them only three minutes to score the second with Raphinha assisting Lewandowski, who nodded home from close range. The Polish striker extended their lead in the 66th minute from just inside the box and Lamine Yamal wrapped up another demolition job by Barcelona in the 77th minute.