Slavisa Jokanovic believes Fulham "paid an expensive price" with their second-half performance as Everton stormed to a 3-0 win.
After half-time, a double from Gylfi Sigurdsson and a Cenk Tosun header saw the points stay at Goodison Park on Saturday, with Fulham's best chance coming when Ryan Sessegnon hit the crossbar before the break.
Jokanovic conceded that Fulham were below par in the second period, and they should have capitalised on their earlier chances.
Sigurdsson double sees off Fulham
"We dominated for the first 45 minutes... We had clear chances to score a goal. The second half, we didn't play well enough and we didn't find the chances," he told Sky Sports.
"After the first goal, we had one really good chance but it is a day for a little bit more speed, to have more power and score three easy goals.
"At the minute, we are learning many things. We must show more solidarity and work even harder. This is the highest level in world football and cannot sleep for so many minutes on the field.
"In the second half, we paid a really expensive price. We must learn and continue with the process and start to be more competitive. To concede in the games is not acceptable and it is going to be really hard for us."
Fulham once again rotated their defence and were forced into an early change when Timothy Fosu-Mensah fell heavily on his elbow and was replaced by Cyrus Christie in the eighth minute.
Speaking about the effect on his defence on Saturday, Jokanovic added: "It is not the best news for us that after a few minutes, we changed our full-back in an area of the pitch where they move really well, but it is part of the competition and we must be ready for anything."