Slavia Prague scored a dramatic stoppage time equaliser to leave Arsenal's Europa League ambitions hanging in the balance.
But Tomas Holes headed home in the dying moments of the game from close range to give Slavia Prague a precious away goal.
The second leg in Prague takes place next Thursday (20:00 BST) and Gunners boss Mikel Arteta, despite his side conceding so late, still believes they will progress to the semi-finals.
"The mindset has to be to go there and score goals and win the game because we have to score if we want to go through," said the Spaniard.