Sarri, who replaced Antonio Conte in the off-season, went unbeaten in his first 18 games in all competitions but has won just six of 12 games since January 1.
"I can understand the situation and our fans, because the result wasn't really good," Sarri said. "We are out of the FA Cup, so I can understand. But I am worried about our results.
"We were unlucky. In the first half, we played better than the opponent and, at the end of the first half, it was 2-0 to them, so we played confused football in the second half.
"But, in the first half, we played well. We need, of course, more aggression, more determination."
Sarri's first two substitutions drew sarcastic applause from Chelsea fans and the last provoked chants of "you don't know what you're doing", followed by "you're getting sacked in the morning".
FA Cup draw
Quarter-finals, March 15-17
Millwall v Brighton
Swansea v Manchester City
Watford v Crystal Palace
Wolves v Manchester United
- AP