Maurizio Sarri praised Chelsea's mental strength as they snatched a 3-2 win over Arsenal on Saturday despite squandering a two-goal lead in a "horrible" period that left the Blues boss squirming on the touchline.
Chelsea looked on course for an easy win over their London rivals after Pedro and Alvaro Morata put them 2-0 up after just 20 minutes at Stamford Bridge.
But the Blues switched off at the back, allowing Arsenal to equalise through goals from Henrikh Mkhitaryan and Alex Iwobi.
Shrugging off that collapse, Chelsea secured their second successive victory under new boss Sarri thanks to a controlled second-half display capped by Marcos Alonso's 81st-minute winner.
"We did very well for 75 minutes but inside that, 15 minutes were horrible," Sarri said.
"It was very, very difficult because we lost the distances between the players and we were unable to cover the lost balls and press like a team, so we were really in trouble.
"But I think the players were really very good because at 2-2 it was not easy with Arsenal.
"In the second half we did very well also mentally."
Alonso's late intervention was a hammer blow for Arsenal, who have lost both matches under their new boss Unai Emery.
The Spaniard conceded Arsenal paid the price for failing to keep Chelsea under pressure in the second half, but he took heart from their initial fightback.
"Our reaction was good. We had chances to go 2-2 and we deserved to score more by half-time," he said.
"In the second half we needed to continue this control, but I think we don't push and keep possession like we did in the first half.
"In our moments, our chances, we didn't do it, and they did.
"That is why the result is 3-2. But it is one process. In the second half we played with two midfielders, 19 and 21 years old.
"They improve and are continuing. I am happy despite the result."