Marcus Alonso's late winner meant Chelsea took a big step toward the Europa League semifinals, despite a display that was far from fluent as several fringe players failed to take their chance to impress.
Chelsea are in control of this tie thanks to Alonso's away goal and will be confident of booking their place in the final four at Stamford Bridge next week. Maurizio Sarri also got away with making seven changes ahead of a Premier League visit to Liverpool on Sunday.
There will be no positive memories of this sloppy and unimaginative display, in which Chelsea created little to make them worthy of victory.
Manager rating out of 10
7 -- Sarri picked several out-of-form players in the hope they could get the job done and was just about proved right. He was forced to use Eden Hazard, N'Golo Kante and Ruben Loftus-Cheek off the bench in the second half, but all three should be fresh enough for Anfield.
Player ratings (1-10; 10 = best. Players introduced after 70 minutes get no rating)
GK Kepa Arrizabalaga, 7 -- A mixed bag. He made impressive saves to deny Ibrahima Traore and Jan Boril in the second half, but several of Kepa's best contributions were made necessary by his own mistakes. For example, he needs to learn to catch, rather than punch, when dealing with high balls.
DF Cesar Azpilicueta, 7 -- Provided valuable defensive grit in the absence of much quality and the fact that he never seems to need a rest continues to amaze. Defended with his usual tenacity and commitment, even if his crossing left a little to be desired.
DF Antonio Rudiger, 8 -- His experience and force of personality were particularly important as Andreas Christensen's performance level fluctuated. Rudiger was also denied a goal only by a superb Ondrej Kolar save.
DF Andreas Christensen, 6 -- Has spoken repeatedly about his difficulty adapting to a lack of regular starts under Sarri and, while he was solid enough overall, his lack of rhythm showed at times when he was a step slow to react to danger or passive in physical duels.
DF Marcos Alonso, 7 -- There were enough defensive concerns to underline that the blip in form, which saw him dropped for Emerson Palmieri, is not over. Alonso's instincts in the final third remain uncanny, however, and he timed his run perfectly to nod in Willian's cross.
MF Mateo Kovacic, 5 -- This was not a performance to answer those who question what he brings to a successful midfield. Kovacic showcased nice close control under pressure, but his passes were never more than safe and his rare dribbles resulted in nothing of note.
MF Jorginho, 6 -- Looks better when he has movement around and in front of him, so it was no surprise that he underwhelmed here. His most ambitious passes rarely found their targets, while Slavia managed to find space around and behind him in transition.
MF Ross Barkley, 5 -- Has been overtaken by Loftus-Cheek as the third midfield starter for games that matter most and, on this evidence, it is easy to see why. One early shot that went over was the extent of Barkley's goal threat, while his passing was inconsistent and indecisive.
FW Pedro Rodriguez, 5 -- Continues to suggest that, despite his best efforts, he is past his prime. Can always be relied upon to work hard and carry out tactical instructions, but his work on the ball was poor and he offered nothing in the final third.
FW Olivier Giroud, 6 -- He has made this competition his stage this season, but did not get anything like the service he requires from an uninspired midfield. One trademark layoff to put Willian through was a rare bright spot on an otherwise frustrating night.
FW Willian, 8 -- Produced the only quality moment of a dire first half -- his rocket of a curler crashed off the bar -- and also embarked on a couple of dangerous dribbles. Combined better with Giroud once Hazard was introduced and eventually created the breakthrough with a pinpoint cross for Alonso.
FW Eden Hazard, 7 -- Brought on for Pedro just shy of the hour mark and his introduction immediately lifted those around him. Produced a couple of sparkling dribbles without directly contributing to Chelsea's winner.
MF N'Golo Kante, NR -- Helped steady the ship when he replaced Kovacic, using his peerless destructive instincts to disrupt Slavia's attempted late surge.
MF Ruben Loftus-Cheek, NR -- Carried the ball skillfully and powerfully down the left flank once in the final 15 minutes, but otherwise did nothing of note for good or bad.