Apparently it takes more than a hat-trick against the champions of Belarus to impress Maurizio Sarri. It is a manager’s job to nitpick and he found imperfections in the performance of Ruben Lotus-Cheek, who scored all three goals as Chelsea sauntered to victory over Bate Borisov.

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The result leaves Chelsea well on course for the next stage of the Europe League, with maximum points from their three group games but Sarri suggested Loftus-Cheek is still some way off a regular place in the first team, although he is at least getting closer.

The England midfielder has been frustrated at being restricted to 33 minutes of Premier League action this season and began as one of eight alterations to the lineup who began Saturday’s draw with Manchester United. “He is improving,” Sarri said. “I told him at the beginning of the season he is a very good player and I think now maybe he is becoming more suitable to my football.

“In the offensive phase he was wonderful but I think he needs to improve the defensive phase. But not only him. We have four midfielders for two positions and three of them have the same characteristics.”

Sarri explained that Loftus-Cheek is competing for a place with Mateo Kovacic and Ross Barkley, with Jorginho seemingly a surefire starter. “Only [N’Golo] Kanté is a defensive midfielder, so it is very difficult to put in so many players of the same characteristics. I hope to be able to do so in the future but I need the cooperation of the players.

Facebook Twitter Pinterest Aleksandr Hleb (right) turns away from his Chelsea’s Mateo Kovacic and his former Arsenal team-mate Cesc Fàbregas. Photograph: Nick Potts/PA

“It’s a very difficult tactical problem to solve without an improvement in the defensive phase. We need to work.”

Loftus-Cheek indicated he is willing to do exactly that. “The first thing is to train well and as hard as I can. Keep the good habits, eat well and sleep well and if I keep doing that the chances will come,” he said.

While Sarri wants Loftus-Cheek to do better when not in possession, he could have no quibble with what the 22-year-old did with the ball. It took him less than two minutes to open the scoring. Davide Zappacosta scurried down the right and aimed a low cross towards the penalty spot, where Loftus-Cheek was free to sweep it into the net for his first goal of the season.

He claimed his second six minutes later, redirecting Willian’s outswinging corner into the net from the edge of the six-yard box. He completed his hat-trick nine minutes into the second half, guiding a side-foot effort from the edge of the area past a feeble dive by the goalkeeper. That brought a delighted reaction from the home crowd, who serenaded their academy graduate with chants of “he’s one of our own”.

Amid the celebrations Marco Ianni, the coach who riled José Mourinho on Saturday, sat in the dugout, on his best behaviour.

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The cheers from the crowd grew louder on the hour, when the gifted 17-year-old Callum Hudson-Odoi was introduced for his first appearance of the season. It was all great fun for the home side until, much to Sarri’s annoyance, Chelsea’s intensity sagged and Bate were allowed to score a late goal. Aleksei Rios crept in unnoticed at the back post to turn in a free-kick from Igor Stasevich.

That sort of sloppiness has infected Chelsea’s otherwise excellent performances under Sarri and he has expressed a determination to eradicate it.

For all that the outcome was never in doubt. Bate may be on course for a 13th consecutive domestic title but they had nowhere near enough quality to threaten a first defeat on Sarri in his 13th competitive match in charge of Chelsea.

The Belarusian club’s only previous trip to London – to Arsenal last year – had ended in a 6-0 thrashing and for a while a repeat of that scoreline looked likely.

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Aleksandr Hleb, the 37-year-old in the heart of their midfield, had joked in the buildup about how much he was looking forward to renewing acquaintances with Cesc Fàbregas, quipping he would take this opportunity to land a sneaky punch on his former Arsenal teammate. But Bate seldom got within touching distance off the home side, and once Loftus-Cheek landed the first blow the contest was over.

Several other Chelsea players had chances to join Loftus-Cheek on the scoresheet. Pedro had a shot deflected just wide, while a header from Gary Cahill was cleared off the line and Kovacic stabbed wide from close range.

William was a constant delight, except when he overhit a pass that would have put Olivier Giroud clean through. Giroud was later denied by a superb one-handed save by Denis Scherbitski.