The defender scored the winner to clinch a 2-1 win over Ecuador on the second anniversary of Diop's tragic early death following a long illness, taking Senegal through in second place in Group A.
Koulibaly also paid tribute to Senegal's 2002 World Cup hero by having Diop's number 19 written on his captain's armband.
Diop scored the winning goal in the stunning 1-0 triumph over France in the opening game of that tournament 20 years ago, helping Senegal reach the quarter-finals.
"Today is the anniversary of his death, I will give his family the trophy in his honour," Koulibaly told reporters.
"We knew the anniversary of his death was something very important, for his family.
"We wanted to pay homage to him, he made me dream when I was a boy.
"We knew we wanted to play in his honour, this wasn't something we were going to let slip.
"It was important for us as a team to make our families and Papa's family proud.
"Now we know we need to rest up, keep a cool head, yes we've qualified, and yes we can savour the win, but now we need to concentrate.
"We need to show why we are the champions of Africa. We need to rest up and get the best from ourselves in the knockout stages."
Koulibaly's goal sent Senegal into the knockout phase for only the second time in their history.
"This was a special day for Senegal, all Senegalese football won today," Koulibaly said on television after the game.
"I'm glad I scored this goal, it's a huge honour for me."
Ismaila Sarr sent Senegal ahead in the 44th minute with an ice-cool no-look penalty after he was felled by Piero Hincapie.
Ecuador fought back through Moises Caicedo's header, but Chelsea defender Koulibaly stroked home three minutes later to send Senegal through with his first goal for his country on his 67th appearance.
Koulibaly also sent a message to his friends in Italy, where he played for Napoli for eight years, after landslides on Monday on the island of Ischia, near Naples
"There were a lot of deaths caused by landslides... I want to dedicate this goal to them today, to give them strength in testing times," added the 31-year-old.
Check the 2022 World Cup schedule and groups standings.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)