They produced an electrifying performance, one of their best this season, to secure victory and drop their city rivals to 19th, four points from safety with four games remaining.
Barcelona took the lead via Lewandowski, who finished from close range after a superb pass from Alejandro Balde.
The second goal was scored by the left-back himself, with Pedri sweeping a cross to the back post for him to pounce on.
According to the videos, it's unclear what happened in the crowd to cause the reaction, but Swift is seen starting "Bad Blood" - maybe an appropriate song for the occasion - without a hitch immediately after the interruption.
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CNN reached out to Lincoln Financial Field and a Swift spokesman for comment.
The concert on Saturday wasn't entirely devoid of bad blood. Other social media videos appear to show thousands of ticketless Swifties gathered outside the open-air stadium to sing along from afar during the event in a heartfelt show of support for their "Anti-Hero."