An 86th minute Marcos Alonso header gave the Blues an advantage going into the second leg at Stamford Bridge
Maurizio Sarri lauded Chelsea's spirit after they stole a 1-0 win at Slavia Prague despite a poor performance on Thursday.
The Blues lead their Europa League quarter-final tie after the first leg thanks to Marcos Alonso's late header, but they were outplayed for long periods away from home.
Sarri said he had always expected a stern test against Slavia but was pleased to see Chelsea show their character by staying in the game and then getting a potentially pivotal away goal.