Chelsea's Marcos Alonso celebrates scoring their first goal with Olivier Giroud and Antonio Rudiger. Photo: Reuters/Paul Childs

PRAGUE – Marcos Alonso's header four minutes from time gave Chelsea the edge over hard-working Slavia Prague with a 1-0 win in the first leg of their Europa League quarter-final in the Czech capital on Thursday.

The Spanish left-back capitalised on a fine cross by Brazilian winger Willian, the tireless mastermind of Chelsea's attack on a chilly night.

Willian himself came close to scoring on 25 minutes but slammed his right-footed effort onto the crossbar.

“We knew very well that to play here is really very difficult,” Chelsea coach Maurizio Sarri told reporters, pointing out Slavia's “very physical and aggressive” style.

“We had to face difficulties during the match. We were able to face them well and then in the second half we were able to play better.”

“We need to think that the second leg will be difficult because these opponents are really very dangerous also away. We need to be careful,” Sarri added.

The Italian made seven changes from Monday's 2-0 Premier League win over West Ham, and Chelsea took some time to warm up.

Those left on the bench included Eden Hazard, who is being touted as a possible £100 million (116 million euros, $131 million) summer transfer target for Real Madrid.

Slavia had the first scoring chance but captain Simon Deli narrowly missed with a diving header from former Chelsea player Miroslav Stoch's free-kick two minutes into the game.

The Czech league leaders had a rare shot on goal in the first half as Petr Sevcik saw his long-range strike stopped by away goalkeeper Kepa Arrizabalaga.

When Chelsea managed to break through the solid Slavia defence, it was through Willian on the left flank, but his ideas found little response from his teammates throughout the opening period.

'Step forward' 

Hazard came on in the 59th minute and his introduction breathed life into Chelsea.

But German centre-back Antonio Rudiger saw his shot saved by Slavia keeper Ondrej Kolar and then headed wide, while Willian flashed wide with a low shot.

Slavia kept Arrizabalaga busy shortly before conceding the only goal, as the Spanish 'keeper stopped Ibrahim Traore's blast before diving to parry away Jan Boril's acrobatic left-footed attempt.

"I'm really happy with the result and also with the performance,” Sarri said, praising the team for its valiance. “In the past when we were in trouble we conceded immediately a goal. Now we are able to... fight and to suffer without conceding anything.”

“I think it is a step forward for us.”

Marcos Alonso scores their first goal on Thursday night. Photo: Reuters/Paul Childs
Marcos Alonso scores their first goal on Thursday night. Photo: Reuters/Paul Childs

Chelsea stopped three fans from attending the game after video footage caught them targeting Liverpool striker Mo Salah with racist chants, according to British media reports, the latest in a series of incidents involving football fans across Europe.

“Chelsea FC finds all forms of discriminatory behaviour abhorrent,” the Blues said in a statement published on their website during the game.

“Where there is clear evidence of Chelsea season ticket holders or members involved in such behaviour, we will take the strongest possible action against them.

Sarri praised the club for banning the fans, calling it a “very strong decision,” but declined to elaborate saying he had not seen the video.

Owned by Chinese developer Sinobo, Slavia in turn were without around 2,000 fans banned from the stadium by UEFA over misconduct during their last-32 game against Genk in February.

Agence France-Presse (AFP)