Chelsea manager Maurizio Sarri said the Europa League could "be a problem" later in the season after his side began their campaign with a 1-0 win at PAOK Salonika.

Willian's early goal from Ross Barkley's lay-off was enough for a much-changed Blues side to maintain their winning start to the season in Greece, despite playing in front of a raucous sold-out crowd in Thessaloniki.

This was Chelsea's first Europa League game since winning the competition in 2013 and the victory - their sixth in a row this season - puts them on three points in Group L, level with BATE Borisov of Belarus who won 2-0 away at Hungarian side Vidi.

The Blues return to Premier League action away to West Ham on Sunday (13:00 BST) before facing Liverpool twice in four days - in the Carabao Cup then the Premier League.

"For an English team the Europa League is a very difficult competition," said Sarri. "In Italy, if I play in Greece on Thursday I can ask to play on Monday night, but I have to play again in 63 hours. I don't know in the future.

"It is not a big problem now because we have played only six matches but in the future it may be a problem. I hope to qualify before the last one or two matches of the group stage."

Hazard rested

Sarri made five changes from Saturday's 4-1 win against Cardiff with Eden Hazard, who Sarri says has complained of tiredness twice in the last month, being rested along with David Luiz and Mateo Kovacic.

Willian came off the bench to seal Saturday's win against Cardiff after Hazard's hat-trick while Barkley was also among those to come into the side.

The former Everton midfielder latched on to a Jorginho pass to burst forward from the centre circle and lay off to the left for captain Willian to sidefoot under the outstretched arm of goalkeeper Alexandros Paschalakis.

But while most of the Chelsea players were composed throughout, Alvaro Morata endured a frustrating night after replacing Olivier Giroud up front.

Morata misfiring

Giroud linked up well with Hazard on Saturday and the way his replacement fared only strengthened the case for Sarri to make the Frenchman his first-choice centre forward.

Giroud is accustomed to squad rotation from his time at Arsenal, while Morata's form in front of goal fluctuated last season and he has only scored once in five starts this term.

Chelsea missed a number of chances to make the scoreline more emphatic and Morata was the biggest culprit. The Spain striker headed wide from a Pedro cross before dragging a left-footed shot wide from Antonio Rudiger's throughball.

And after being unable to keep a sidefoot volley down, Morata blazed over left-footed from the left side of the box.

Pedro should have doubled Chelsea's lead from a 38th-minute counter-attack, firing straight at the keeper after being picked out by Marcos Alonso, and from the resulting corner Morata steered a difficult header wide.

He cut a forlorn figure as he trudged off to be replaced by Giroud on 81 minutes.

"Morata had three or four opportunities, he was unlucky," said Sarri. "I hope in the future I can try to help him, but the confidence comes only with goals. I am not able to give him confidence.

"But I have to say also that for the first time this season he was very ready in the box. He was on the ball, he was active."

Match stats

• Each of Chelsea's last 10 managers have won their first European game in charge, with Claudio Ranieri the last to fail to do so in September 2000 (0-2 v FC St Gallen).
• Chelsea have won each of their last four games in the Europa League, a run which includes their final three games in 2012-13 when they won the competition.
• Chelsea manager Maurizio Sarri has won all of his group stage games in the Europa League (seven out of seven), keeping five clean sheets in this run.
• Ross Barkley's assist for Chelsea's goal was his first in club football since April 2017 for Everton against Leicester.
• PAOK have failed to score in six of their last seven home games in the Europa League.

What's next?

Chelsea visit West Ham in the Premier League on Sunday (13:30 BST) before travelling to Liverpool in the Carabao Cup third round next Wednesday (19:45 BST).

In their next Europa League fixtures on Thursday, 4 October, the Blues host Vidi while PAOK are away to BATE Borisov (both 20:00 BST).