Marcos Alonso's late header dragged a lacklustre Chelsea to a 1-0 Europa League win at Slavia Prague.
The Spain full-back ghosted clear in the box to nod home Willian's teasing far-post cross, to hand the Blues the slender advantage midway through their quarter-final.
Chelsea came very close drawing their last-eight first leg tie at the Sinobo Stadium, the Blues struggling for fluency throughout a niggly night in Prague.
Replacement Ruben Loftus-Cheek's smart spin and break turned Slavia's defence at the death however, before Willian served up the perfect cross.
Alonso's third goal of the season and second in the Europa League proved just enough for Chelsea then, but the Stamford Bridge men will hardly be happy with their performance.
Chelsea will now expect to complete the job and move through to the semi-finals when hosting Slavia in the return leg next Thursday.
The Blues were relieved to prevail on the pitch, in another night where racism hit the headlines.
Chelsea's security team identified and barred entry to the stadium for three supporters, who had taken part in a video on social media where Liverpool forward Mohamed Salah appeared to be racially abused.
Three other supporters in the video did not attempt to enter the Sinobo Stadium.
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Line-ups
Slavia Prague XI: Kolar; Coufal, Ngadeu-Ngadjui, Deli, Boril; Traore, Kral; Masopust, Sevcik, Stoch; Olayinka
Subs: Kovar, Zmrhal, Husbauer, van Buren, Kudela, Skoda, Frydrych
Chelsea XI: Kepa; Azpilicueta, Christensen, Rudiger, Alonso; Barkley, Jorginho, Kovacic; Pedro, Giroud, Willian
Subs: Caballero, Kante, Higuaín, Hazard, Loftus-Cheek, Zappacosta, David Luiz
