Barca struggled in the first half, but ultimately emerged victorious 4-2 after a better second-half performance.
The hosts stunned Barca in the 10th minute when Vasil Kusej met Tomas Holes' header from a corner. Kusej's low shot beat Barca goalkeeper Joan Garcia, giving Slavia Prague a 1-0 lead.
It took the visitors almost half an hour to equalize. Fermin Lopez made it 1-1 in the 34th minute with a foot-to-foot combination, tapping in Frenkie de Jong's through ball.
Eight minutes later, the young Spanish star scored a brace from distance after receiving a pass from Pedri. Fermin's powerful and precise shot tore through Slavia Prague's net for the second time, giving Barca a 2-1 lead.
Just as they were about to close out the first half with the lead, Barca conceded. Starting from the same situation as Slavia Prague's first goal, a corner kick, Robert Lewandowski mishandled the ball. He attempted to clear the ball but instead scored into his own net in the 43rd minute. The score was 2-2, and the first half ended.
