The Blues' manager admitted they were awful in the first half at the Emirates.
Frank Lampard was happy with how Chelsea beat Arsenal at the Emirates Stadium on Sunday.
The Blues' manager admitted they were awful in the first half when Pierre-Emerick Aubameyang scored the opener, but he was delighted they had the 'spirit and desire' to turn the game around as late goals from Jorginho and Tammy Abraham handed the west London club a 2-1 win in the London derby.
"We were so awful for 30 minutes; slow, lethargic, nervous, the opposite of against Tottenham," he told BBC Sport. "We gave Arsenal everything they wanted.
"We made the change early, felt it had to be done. In the second half, we dominated.
"After 10 minutes or so, it was clear that Arsenal had seen us play against Tottenham and made us into a back five instead of a back three.
"They were on top and there was a lack of balance to our team. The sub gave us another man in midfield and gave us more urgency.
"From my point of view, you can accept a missed pass but you can't accept lethargy in a London derby. The players were told that [at half-time] and they delivered.
"The second half was nothing to do with tactics, it was all to do with spirit and desire."
He added: "I still haven't bounced back from Boxing Day mentally. In our next home games, we'll do everything we can to turn the corner.
"We're still in fourth and want more, and the home games have been different so we have to focus on them when they come around."