Casillas gave the king a Spain shirt with the No. 1, signed by the entire team.
“The country is more united and people can forget their problems for a while,” said 27-year-old Jessica Pino in a team shirt, draped in the Spanish flag and with a Viking hat in the national colors.
The party erupted from the end of the first half of the match on Sunday night, when Spain were already 2-0 up, and huge numbers of fans invaded the Plaza de Cibeles.
The victory sparked a new sports-related record for tweets per second, Twitter said.
The match resulted in 16.5 million tweets from fans around the world and total global traffic on the platform peaked at 15,358 tweets per second during the fourth goal, a new sports-related record on Twitter, the company said.