Chelsea took complete control of the first half of their second leg Europa League game against Slavia Prague by beating them 4-1.
However, Sarri’s boys showed a weak performance in the second half that made the visitors score two goals to make it 4-3, making Chelsea narrowly escape with a win to qualify for the semi-final.
Sarri, however, was not pleased with their second half start and said that they really need to make improvements to be able to win the trophy.
“As usual in the last two months, we started badly in the second half. We need a solution to solve this problem.
“In the last 10 matches, we started like in this match. It’s a big problem but we have to consider the match and the qualification.
“At the end of the first half, we thought we were qualified but against this opponent. This wasn’t true because they are physical. I’ve never seen anything like that in the last 20 years.
“It’s true, the second half could have been difficult for us and we did something wrong. But of course, we are happy because to get into a European semi-final, it’s not easy so we are happy.
“The target was to start [the second half] with the same application and intention… but we didn’t do it.
“I don’t know and it’s not easy to understand, otherwise we can start the problem easily. It’s difficult to understand why.”
Eden Hazard, the subject of a couple of clattering early challenges, was taken off midway through the second half, but Sarri hopes he will be fit to face Burnley on Monday Night.