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
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Slavia Prague vs Chelsea suspensions
The Czech side have five players who are one booking away from a suspension tonight. Box-to-box midfielder Ibrahim Traore, the match-winner against Sevilla, would miss the second leg in London if booked, alongside Jan Boril, Ondrej Kudela, Peter Olayinka and Skoda.
Ross Barkley is the only Chelsea player at risk of suspension but with Mateo Kovacic and Ruben Loftus-Cheek able to deputise, it wouldn't pose a serious problem for Maurizio Sarri if he is cautioned.
And here is the Eden Arena, now known as the Sinobo Stadium.
Eden Hazard is here but starts on the bench - and Slavia Prague will be hoping it stays that way.
Chelsea do have history here; they played in Prague in the 2013 UEFA Super Cup where they lost on penalties to Bayern Munich. The Blues' fans can rest easy though, knowing there's no chance of that happening again tonight.
Photo: Reuters
It's blue skies in north London as Arsenal fans make their way to the Emirates Stadium with around 45 minutes until kick-off.
Photo: PA
Koscielny returns; Aubameyang AND Lacazette start
Arsenal coach Unai Emery is going for broke in the first leg against Napoli after opting to start Alexandre Lacazette and Pierre-Emerick Aubameyang together.
The pair have enjoyed a decent record when playing together and make up part of the front three in a 3-4-3 setup, with Mesut Ozil providing creative support from the right.
Aaron Ramsey starts alongside Lucas Torreira having recovered from a knock and captain Laurent Koscielny is back in the starting XI after being ruled out previously with a bruised foot.
Sarri rotates; no Hudson-Odoi in the squad
Chelsea coach Maurizio Sarri has made seven changes to the team that beat West Ham 2-0 on Monday.
Eden Hazard is rested ahead of the weekend clash with Liverpool while Callum Hudson-Odoi is not in squad, despite travelling to Prague with the rest of the team.
Pedro and Willian come into the side in place of Hazard and Hudson-Odoi while Olivier Giroud, the competition's top scorer with nine goals, starts ahead of Gonzalo Higuaín.
There are also changes at the back with Andreas Christensen starting at centre-back and Marcos Alonso filling at left-back, with David Luiz on the bench and Emerson left out entirely.
Finally, Mateo Kovacic makes up the three-man midfield with N'Golo Kante handed a rare night off.
Team news: Arsenal vs Napoli
Arsenal XI: Cech; Sokratis, Koscielny (c), Monreal; Maitland-Niles, Torreira, Ramsey, Kolasinac; Ozil, Lacazette, Aubameyang.
Subs: Leno, Elneny, Mkhitaryan, Iwobi, Mustafi, Suarez, Guendouzi.
Napoli XI: Meret; Hysaj, Maksimovic, Koulibaly, Mario Rui; Callejon, Allan, Fabian, Zielinski; Insigne (c), Mertens.
Subs: Ospina, Malcuit, Ghoulam, Chiriches, Ounas, Younes, Milik.
Team news: Slavia Prague vs Chelsea
Slavia XI: Kolar; Coufal, Ngadeu-Ngadjui, Deli (c), Boril; Traore, Kral; Masopust, Sevcik, Stoch; Olayinka.
Subs: Kovar, Zmrhal, Husbauer, van Buren, Kudela, Skoda, Frydrych.
Chelsea XI: Kepa; Azpilicueta (c), Christensen, Rudiger, Alonso; Barkley, Jorginho, Kovacic; Pedro, Giroud, Willian.
Subs: Caballero, Kante, Higuaín, Hazard, Loftus-Cheek, Zappacosta, David Luiz.
Chelsea coach Maurizio Sarri set to make several changes to his side against Slavia Prague after the 2-0 win over West Ham, with Eden Hazard likely to be handed a rest.
But Arsenal coach Unai Emery knows he must field his strongest XI if he wants to beat Napoli after their defeat to Everton at the weekend saw them drop out of the top four.
Team news should be arriving shortly, so stay tuned!
Slavia Prague vs Chelsea: How the teams could line up
Olivier Giroud will once again spearhead Chelsea's attack as they look to take a first leg advantage in their Europa League last 16 tie against Slavia Prague.
The France international has nine goals in seven starting appearances in this competition this season and while opportunities in the Premier League remain limited, he has been Maurizio Sarri's go-to man in European competition.
GettyCallum Hudson-Odoi and Ruben Loftus-Cheek have also often relied on the Europa League for starting appearances this season but after playing 85 and 70 minutes respectively against West Ham on Monday night are likely to be rested tonight.
The same could also apply for Eden Hazard, who has played just 117 minutes in this competition this season.
Andreas Christensen, another to have featured regularly on Thursday nights, is also poised to return to the starting XI after recently declaring his intention to stay and fight for his place at Stamford Bridge.
Predicted line-ups
Chelsea (4-3-3): Kepa; Zappacosta, Rudiger, Christensen, Alonso; Kante, Kovacic, Barkley; Pedro, Giroud, Willian
Slavia Prague (3-5-2): Kolar; Kudela, Ngadeu-Ngadjui, Deli; Coufal, Traore, Stoch, Kral, Boril; Masopust, Zmrhal
Arsenal vs Napoli: How the teams could line up
Pierre-Emerick Aubameyang is set to return to the Arsenal starting XI for their Europa League quarter-final first leg clash against Napoli tonight.
Aubameyang has started his side’s last two matches on the bench with Unai Emery revealing at a press conference on Wednesday his striker has been taking antibiotics to combat a virus.
The Arsenal boss expects the 29-year-old to be fully fit to face Carlo Ancelotti’s side on Thursday evening, where he could join Alexandre Lacazette in attack.
Mesut Ozil meanwhile could miss out again with Aaron Ramsey set to return.
The Wales midfielder was only fit enough to play the second half of Sunday’s 1-0 defeat at Everton due to a groin problem but is expected to be available tonight.
Laurent Koscielny (foot) and Granit Xhaka (groin) face fitness tests having also both missed out at the weekend.
Arsenal XI to face Napoli: Cech, Mustafi, Sokratis, Koscielny, Naitland-Niles, Torreira, Xhaka, Kolasinac, Ramsey, Aubameyang, Lacazette
Napoli XI to face Arsenal: Meret, Hysal, Koulibaly, Maksimovic, Mario Rui, Callejon, Allan, Ruiz, Zielinski, Milik, Mertens