The teen ended Daniil Medvedev's 19-match win streak with a 6-3 6-2 hammering on Sunday to leapfrog Novak Djokovic, who is not competing in the US hardcourt swing as he cannot enter the country due to not being vaccinated against COVID.
Djokovic had taken top spot in the rankings by winning the Australian Open, with Alcaraz missing the year's first Grand Slam due to abdominal and hamstring injuries.
The Spaniard returned to the ATP Tour in February at Buenos Aires where won his first title since last year's US Open and made the Rio final before withdrawing from Acapulco with a strained hamstring.
"I began the season well but struggled a lot with injuries," Alcaraz, who defends his Miami Open title this week, told Tennis Channel. "Two injuries in the legs in about four months, it was tough to stay strong mentally.
"I missed some tournaments I wanted to play, but I worked really hard with my team. I believe in myself and the work I'm doing right now and I'd say that's the most important thing.
"It means a lot to recover the number one ranking. I'm not going to say it was easy, but it was easier because Djokovic was not playing."
Victory over Medvedev meant Alcaraz became the youngest man to win the Indian Wells and Miami Open titles, a feat dubbed the 'Sunshine Double'.
"The thing that's improved most is the mental game," said Alcaraz, who lost to Medvedev in their first meeting in 2021.
"I got a lot of experience since that match. I was new on Tour at that time but now I've played a lot of great matches and won great titles. That's made me more confident," Alcaraz said.
"Now I know how to handle tough moments."
