Chelsea head coach Maurizio Sarri was relieved to advance in the Europa League after enduring a disappointing performance from his team while battling a fever in Belarus.

Olivier Giroud's first Chelsea goal since May, and 794 minutes of playing time, earned a 1-0 victory at BATE Borisov and a fourth win from four Group L games.

The Blues remained unbeaten in 17 competitive games this season, qualifying for the last 32 with two matches to spare.

"I was in trouble," Sarri said.

"I had fever. It was a very hard day for me. I don't know if I am improving or if it is only the temperature."

Freezing fog in Borisov contributed to an underwhelming display.

"The best situation is the result. We didn't play very well," Sarri added.

"It wasn't very easy to play a good game here. There was all the conditions to play very badly, for the cold, for the opponents, for the pitch, for everything. I think we could have done better.

"I didn't like the first half. We moved the ball only horizontal and slowly. It was really very difficult to be dangerous.

"Better in the first 20, 25 minutes in the second half. Then we managed not really very well the last 15 minutes."

BATE, comfortably beaten last month in London, struck the frame of the goal three times, including deep in stoppage time, and Eden Hazard's services were required for longer than anticipated in Belarus.

As the game clicked into the 51st minute, Hazard was fouled and sent the resulting free-kick soaring out of play beyond the far post.

Hazard had been due to be off by then and Sarri was gesticulating wildly in his technical area, apparently towards the Belgian.

Giroud struck moments later, heading in Emerson Palmieri's cross at the near post.

Giroud told BT Sport: "It's true, I was hoping to score soon because I came back late from the World Cup and lacked a bit of luck. You always have to work hard and keep the faith."

Sarri added: "I'm pleased for him. He's a very important player for us, because he's a very, very useful player for the team.

"But I know very well strikers want to score. And so for his confidence I think it's very important.

"But, I don't want him to be worried about scoring, because for us he's very important, very useful."