Alcaraz, 19, defeated 23-year-old Ruud 6-4, 2-6, 7-6 (7-1), 6-3 in a match that took over three hours.
Alcaraz becomes the youngest men’s singles grand slam winner since compatriot Rafael Nadal won the first of his major titles in June 2005.
“This is something I’ve dreamt of since I was a kid. To be No. 1 in the world, to be a champion,” Alcaraz said, adding he thought about some of his family members who couldn’t make it to watch him play.
“I always say it’s not time to be tired in the final round of the grand slam, you have to give everything you have inside,” he said.
Ruud said he’ll continue chasing the No. 1 spot.
“Today was a special day, both Carlos and I knew what we were playing for and both knew what was a stake,” Ruud said. “I’m disappointed of course that I’m not No. 1, but No. 2 isn’t so bad either.”
“It’s the final of a grand slam, fighting for the No. 1 in the world — something that I have dreamed of since I was a kid,” Alcaraz told reporters early Saturday after defeating Frances Tiafoe in the final four.
A clay court specialist, Alcaraz has drawn comparisons to 22-time grand slam champion Nadal and is just the second player in the Open Era to make the US Open final in his teens after Pete Sampras.
“Right now, you can see that all the hard work I put in every day is paying off,” Alcaraz told reporters early Saturday.